How are the clusters “μψ” and “γξ” pronounced in Modern Greek?

Modern Greek has nasal Sandhi. That means that following a word ending in /n/, any voiceless stop is voiced. (And in the case of /ks/ and /ps/, so is the following /s/.) The /n/ in turn assimilates in place of articulation to what follows.

So:

• patera “father”, san patera [sam batera] “like a father”
• keo “I burn”, ðen keo [ðeŋ ɡeo] “I don’t burn”
• psixi “soul”, stin psixi [stim bziçi] “to the soul”
• kseno “stranger”, ton kseno [toŋ ɡzeno] “the stranger”