I know this is an old thread...that said...
Parts of the Slavonic version of this hymn is stuck in my head, as we often sing it at Feasts of the Cross. However, I've never seen this written in Cyrillic font. I'm learning Russian, and find it much easier to figure out the pronunciation in Cyrillic than in a transliteration (which has always confused me). I'm also probably mispronouncing the parts I remember.
I'm having an awful time finding the Slavonic version of this hymn online. If anyone could post the Slavonic version of the hymn here in Russian characters, I would be very appreciative! Thanks!

I can't find it either, but on this one you are in luck, the pronunciation is as it appears in the transliterated form, there are no hard marks or 'schs' to worry about, at least in the more Ukrainianized accent of Slavonic. Can't help if you are looking for the Russian accented slavonic though...
Kres-
tu (accent on second syllable)
Tvoj-e-mu (accent on first syllable)
pok-la-nja-
jem-sja (main accent on last syllable)
Vla-
dy-ko (accent on second syllable)
i svja-
toj-je (accent on 'toj')
vos-kre-
se-ni-je (minor accent on 'vos', main accent on 'se' )
Tvo-
je (accent on second syllable)
slav-im. (accent on first syllable)