So I’ve been studying this bit of text for the past few days, trying my best to make sense of it. It comes right at the beginning of Eusebius’ Commentary on the Psalms. I’ll give my translation with some notes, and then the Greek text and the Latin translation that appears in Migne’s Patrologia Graeca vol 23.
This bit appears in PG 23.66
Eusebius on the Inscriptions of the Psalms. Some Abbreviated Teaching.
There are 150 psalms, and the number 50 is holy. For Pentecost has 50 days, and there are 50 years for a Hebrew Jubilee . Nabla is what the Hebrews call their harp, and it is the only true musical instrument. It is not played from the lower parts, but its supporting metal is on top. The “Psalms”  then are only struck up with this instrument, not with a voice. But an “Ode” begins with a harmonious voice. An “Ode of the Psalm” begins by the instrument of a harmonious voice. A “Psalm of the Ode,” on the other hand, leads in with the sound of the striking of strings. By way of allegory, a psalm is like the harmonious movement of the body, moving to good works,  although some do not follow such contemplation. Singing without praxis is like the mind’s direct perception of truth, where one’s soul is enlightened about God and his oracles. But an “Ode of the Psalm” leads us to the practice of knowledge, as it is written, “if you desire wisdom, keep the commandments, and the Lord will supply it to you.” For a “Psalm of the Ode” leads us to praxis accompanied by knowledge. It instructs us how and when things must be done. Therefore they are the first among the inscriptions. For the holy one does not begin from theory, but always faithfully runs to praxis. Many of the odes are “To the End.” Whenever there is “Steps,” in the inscription, there is never the word “Psalm,” nor does it stand alone or mixed with others. It always stands with “Ode.” For the “ascent” only perceives the abstract. Selah is not found in Aquila or the Hebrew, but apart from him it is always found.
 I have no idea how to get this from the Greek, but the Latin translator interpreted it thus.
 That is, Psalms which have the word “psalm” in their inscription (which is not everyone, some have “ode”, some have nothing, etc.).
 Greek: εἰς ἐργασίαν ἀγαθὴν. ἐργαίαν can also have the meaning “artistic production,” and Eusebius may have that in mind, though I think “good works” fits better with the following context.
 Sirach 1:26
 I don’t know what he means by “Therefore they are the first among the inscriptions.” The Greek here is: διὸ καὶ πρῶται τῶν ψαλμῶν αἱ ἐπιγραφαί. I have left it vague in English, but if I had to I would perhaps make it “Therefore they are the finest of the inscriptions.”
 Greek: ἡ ἀνάβασις, which as far as I can tell is a Greek philosophical term describing the soul’s ascent to God. Here, it stands in contrast to the Greek ἁναβαθμοὶ, which means “steps” or “stairs.” Perhaps ἁναβαθμοὶ is conceived as a Christianized ἀνάβασις, which includes both the abstract (θεωρία) and the practical (πραξις.
 Greek: διάψαλμα which translates the Hebrew word Selah.
– I have placed in quotation marks what I believe to be technical terms relating to inscriptions.
– I’ve used “praxis” or “practice” to translate the Greek word πραξις. Without being able to peg down a more specific meaning for it, I think our English word captures enough of the vague antithesis between “theory” and “praxis” (which is definitely present in this passage) to service here. I’m usually leery of doing such a 1-1 translation, but I’ll keep it for now.
– Eusebius seems to make a broad contrasts between “Psalms” and “Odes.” Odes are introduced by singing, while Psalms are introduced by a harp. This can be confusing since all of them are psalms in the looser since (they’re in the Psalter), but he appears to make a technical distinction between the two based on their usage in the inscriptions. “Ode” can also mean “singing” in Greek, and I think that’s in view too. In one place I have translated ᾠδὴ as “singing” (“Singing without knowledge…), otherwise I have left it as a technical term “ode.”
– Eusebius does like allegory and contemplation (in good Platonic and Origenic fashion), but he seems here to be in favor of a healthy mix of “theory” and “practice.” His affinity for philosophy and the abstract doesn’t negate the importance of practical things.
Here’s the Greek for reference:
ΕΥΣΕΒΙΟΥ ΕΙΣ ΤΑΣ ΕΠΙΓΡΑΦΑΣ ΤΩΝ ΨΑΛΜΩΝ. ΕΡΜΗΝΕΙΑ ΤΙΝΩΝ ΚΑΤ’ ΕΠΙΤΟΜΗΝ.
Ἑκατὸν πεντήκοντα τυγχάνουσιν οἱ ψαλμοὶ, ἱεροῦ τοῦ νʹ τυγχάνοντος ἀριθμοῦ·
ἐν μὲν ἡμέραις ποιῶν τὴν Πεντηκοστὴν, ἐν δὲ ἐνιαυτοῖς τὸν παρ’ Ἑβραίοις καλούμενον
Ἰωήλ. Νάβλα δὲ παρ’ Ἑβραίοις λέγεται τὸ ψαλτήριον, ὃ δὴ μόνον τῶν μουσικῶν
ὀργάνων ὀρθότατον, καὶ μὴ συνεργούμενον εἰς ἦχον ἐκ τῶν κατωτάτω μερῶν, ἀλλ’
ἄνωθεν ἔχειν τὸν ὑπηχοῦντα χαλκόν. Ψαλμοὶ μὲν οὖν οἱ διὰ μόνου τοῦ ὀργάνου χωρὶς
φωνῆς ἀνακρουόμενοι· ᾠδὴ δὲ οἱ διὰ φωνῆς ἐμμελοῦς· ᾠδὴ δὲ ψαλμοῦ τὸ τῷ ὀργάνῳ
σύμφωνον ἐπάγειν φωνήν· ψαλμὸς δὲ ᾠδῆς ἀνάπαλιν, προηγουμένης τῆς τῶν
κρουσμάτων φωνῆς. Ἀλληγορίας δὲ νόμῳ, ψαλμὸς μὲν σώματος κίνησις ἐναρμόνιος εἰς
ἐργασίαν ἀγαθὴν, κἂν μὴ πάνυ τις ἐπακολουθῇ θεωρία· ᾠδὴ δὲ χωρὶς πράξεως ἀληθείας
κατάληψις, φωτιζομένης ψυχῆς περὶ Θεοῦ καὶ τῶν λογίων αὐτοῦ. Ὠδὴ δὲ ψαλμοῦ,
προαγούσης πράξεως γνώσεως· κατὰ τό· Ἐπιθυμήσας σοφίας διατήρησον ἐντολὰς, καὶ
Κύριος χορηγήσει σοι αὐτήν. Ψαλμὸς δὲ ᾠδῆς πρᾶξις ὑπὸ γνώσεως ὁδηγουμένη, περὶ
τοῦ πῶς καὶ πότε πρακτέον· διὸ καὶ πρῶται τῶν ψαλμῶν αἱ ἐπιγραφαί· οὐ γὰρ ἀπὸ
θεωρίας ὁ ἅγιος ἄρχεται, ἀλλ’ ἅπαν πίστει ταῖς πράξεσιν ἐπιτρέχει. Ἐπὶ δὲ τῷ τέλει
πολλαὶ αἱ ᾠδαί· καὶ ὅπου ἀναβαθμοὶ, οὐδαμοῦ ψαλμὸς, οὔτε καθ’ ἑαυτὸν, οὔτε μετ’
ἐπιπλοκῆς. Ὠδαὶ δὲ πάντα καθ’ ἑαυτάς· ἡ γὰρ ἀνάβασις πρὸς μόνην ὁρᾷ θεωρίαν.
∆ιάψαλμα δὲ παρὰ μὲν Ἀκύλᾳ καὶ τῷ Ἑβραϊκῷ οὐ κεῖται· ἀντὶ δὲ αὐτοῦ τὸ ἀεί.
And for the Latinists, here’s the Latin translation that appears in Migne’s Patrologia Graeca vol 23. I typed this myself from an image scan, and haven’t done thorough checking, so there are probably several mistakes. It doesn’t help that my Latin’s not that great! There are several scans available. You can find several on google books here.
EUSEBII IN PSALMORUM INSCRIPTIONES. INTERPRETATIO QUARUMDAM COMPENDII MORE DESCRIPTA.
Centum et quinquaginta psalmi sunt : et sane sacer est quiquagenarius numerus, illo siquidem dierum curriculo instituitur Pentecoste, ac totidem annorum numero Jubilaeus, ut vocant Hebraei, celebratur. Nabla apud Hebraeos vocatur psalterium ; quod ex musicis instrunienties solum rectissimum est, neque ab infirmis partibus ad sonum adhibetur, sed a supernis sonanti aere instruitur. Psalmi itaque vocantur quot sola instrunientorum pulsatione, nullis admistis vocibus, persolvuntur. Canticum dicitur quod sauvi aequabilique voce conitur ; canticum psalmi, quod una cum instrumentis consonas admittit voces ; psalmus cantici rursum, cum instrumentorum musicorum sonus vocibus preit. Si allegorice res accipiatur, psalmus est concinnus corporis motus ad opus bonum exsequendum, etiamsi contemplatio parva subsequatur. Canticum nullo opere admistum est veritatis comprehensio, mente ad De ejusque sermonum contemplationem illustrata. Canticum psalmi dicitur cum cognitio actum praecedit, juxta illud : Concupiscens sapientiam, serva maudaia, et Dominus praebit illam tibit. Psalmos cantici est actus ducente cognitione admissus, docente scilicet quo pacio quove tempore sit agendum : quapropter in inscriptione psalmorum vox canticis praeit ; non enim a contemplatione vir sanctus orditur , sed fide omnino ad opera exsequenda currit. Sub finem multa cantica sunt. Ubi autem gradus habentur nusquam psalmus , neque per solus, neque alia adjuncta voce inscribitur : sed ibi cantica solum apponuntur ; nam ubi ascensus graduum est, ibi sola contemplatio spectatur. Diapsalma porru apud Quilam et in Hebraico non estat : sed ejus loco, semper ascribitur.