Krell have confirmed that you can mix inputs on the amp.See response below
" At the end of the day though it is possible to use channels in balanced and in single-ended mode at the same time. Two items of importance to note are:
1 - There will be a 6 db gain differential between the balanced and single ended channels. Meaning that the balanced channels will be louder during surround playback. However you should be able to balance this out by doing a system volume calibration via your processor set up menu.
2 - When operating any balanced amp in single ended you will need to short out the balanced input to make sure that noise does not get introduced through it, the result of which will be a noticeable hum or buzz present when attempting playback. We ship all of our amps with shorting pins (brass U pins) installed in the balanced inputs from the factory. These are inserted into pin 1 and 3 on the balanced input."
" At the end of the day though it is possible to use channels in balanced and in single-ended mode at the same time. Two items of importance to note are:
1 - There will be a 6 db gain differential between the balanced and single ended channels. Meaning that the balanced channels will be louder during surround playback. However you should be able to balance this out by doing a system volume calibration via your processor set up menu.
2 - When operating any balanced amp in single ended you will need to short out the balanced input to make sure that noise does not get introduced through it, the result of which will be a noticeable hum or buzz present when attempting playback. We ship all of our amps with shorting pins (brass U pins) installed in the balanced inputs from the factory. These are inserted into pin 1 and 3 on the balanced input."