Yes I do know that Post-Classic Greek pronunciation is quite different from Ancient Greek, however in the case of the vowel "Υυ" this has not changed as far as we know.

Example,

περὶ ὧν Θισ[β]εῖς λόγους ποιήσαντο· περὶ τῶν καθ᾿αὑ[τ]οὺς πραγμάτων, οίτινες ἐν τῇ φιλίᾳ τῇ ἡμετέρᾳ ἐνέμειναν, ὅπως αὐτοῖς δοθῶσιν [ο]ἷς τὰ καθ᾿ αὑτοὺς πράγματα ἐξηγήσωνται, περὶ τούτου τοῦ πράγματος οὕτως ἔδοξεν· ὅπως Κόιντος Μαίνιος στρατηγὸς τῶν ἐκ τῆς συνκλήτου [π]έντε ἀποτάξῃ οἳ ἂν αὐτῷ ἐκ τῶν δημοσίων πρα[γμ]άτων καὶ τῆς ἰδίας πίστεων φαίνωνται.

[IPA: perì hôːn tʰizbîːs lóɡuːs epojéːsanto; perì tôːn katʰ hautùːs praɡmátoːn, hoítines en tîː pʰilíaːi tîː heːmetéraːi enémiːnan, hópoːs autoîs dotʰôːsin hoîs tà katʰ hautùːs práɡmata ekseːɡéːsoːntai, perì túːtuː tûː práɡmatos húːtoːs édoksen; hópoːs ˈkʷintos ˈmainios strateːɡòs tôːn ek têːs syŋkléːtuː pénte apotáksiː, hoì àn autôːi ek tôːn deːmosíoːn praɡmátoːn kaì têːs idíaːs písteoːs pʰaínoːntai]
The sound is that of an "i" as in "Phisics" as far as this letter is concerned in Ancient Greek.

Good call thought :)