I am having some problems trying to setup my new mixer (EURORACK
UB1204FX-PRO). I have got it connected to the amp and monitors
correctly and I have plugged 3 things in. On channel 1 I have a
Clavinova CLP150. Channel 2 has a Motif ES Rack. Channel 3 has an
intel mac mini (connected via the headphones out).

Only the motif sounds correct when played. The clavinova sounds
distorted when connected to headphones out or aux out. Output from the
mac is also awful - playing a normal cd sounds sounds like it is
cutting all the vocals and percussion out and sounds like some sort of
weird flanging effect. But any combination of cables or channels and
the motif always sounds correct so I know it is nothing to do with the
cables or channels I am using.

The man at the shop thinks it may be to do with using headphones out
but that is the only choice I have on the mac and the clavinova still
sounds as bad whichever output you use.

Any ideas?