Maybe there is a grounding issue with the input cables leading to the Audiolab amp. Have you tried switching these out with another set ?
Perhaps a ground loop is at work here. Does the Audiolab have a grounded mains plug ? - temporarily try it with a cheater to see if that changes things.
The EMF may be propagating into the AL's input path. Try plugging your amp into another sound card jack - even an AUX
input on the sound card card would be ok for testing this theory.
The only other easy path for input beyond mains and signal are the speaker wiring. Your amp is a quality item, so I doubt this is an issue, but try switching the speakers off and plugging your phones into the amp.
Lastly, it could be that this particular printer is defective and an internal EMF filter is not working properly. The high pitched noise, hiss or squeels sound like power supply/motor drive generated switching hash.