The louder you play the more current the amp needs to supply and the more likely that output will have problems.
If you are using a surround sound output you will only hear processed signals not stereo ( say the side channels ). If you are running a 5.1 system with a 7.1 channel receiver you may be able to use the side channels and define them as rear while occupying the zone2/rear channels for your zone2 signals. You will in all probability need to define that amp as zone 2 as opposed to rear channels.
Or you can try any of the systems integrations amps from Niles, Xanteck, Speakercraft. 25-40 watts ought to be sufficient. Obviously should you wish to use a Krell for better sound it would also work
Alan