One of the downsides to bi-amping with a multichannel amp is that if the four channels you are going to use for bi-amping share the same power supply..no gain from reduced load as you would get from seperate amps.
If you add a two channel amp to the mix that matches the Tas's specs you may be very happy with the new setup. I would put the two channel Krell on the bass section of the 802's.
Dave