Al...
Another thought about your increase in your receiver's temperature when
using signal from PC sound card.
Many new receivers/amplifiers have very high slew rates (fast acting
amplifiers) and will try to amplify ANY high frequency "noise" that most
likely you won't be able to hear (above 22khz). This noise comes from
harmonics created from the "digital (0s and1s) to analog (sound)"
conversion. Most low end sound cards do not filter these harmonics out and
allow them to pass along with the "sound".

If you or a friend can get your hands on a scope you can "see" this problem
that you can't hear.

This can be very dangerous to the health of your receiver (amplifier
failure) and/or your tweeters (trying to reproduce this "sound") in your
speakers.

I've seen this problem from very low end units all the way up to brand new
high end commercial installations. (a local Hall of Fame Museum). One of
their Amps was getting VERY hot even when there wasn't any audible "sound"
present. The signal present light on the mixer was lit though. Adding two
filters (left/right) to trap anything above 22khz solved the problem.

Good luck with your problem
Dave McGaffney
KVM Services