is it possible when you hooked up the new amp you let the cables from 1050 to 755 get 'intertwined' with speaker or power cables?
since this wasn't present before,that is the first thing i'd check.
make sure to keep them separate.
as far as the coax from the dvd,they say that is more 'pure' than optical,but they are both virtually immune to interference so it's basically your call.