Two FA-66 daisy-chained - can only listen to either pair of inputs

  Hi, I acquired a second FA-66 (red one, Edirol branded) new for little money and I have it running successfully alongside my first FA-66 (green one, Cakewalk branded) in my DAW PowerStudio 660. The main reason was to be able to connect four mics simultaneously. I also hope to connect an 8-track tape machine to digitize old reels. I'd also like to mic a complete drum kit, after buying the necessary pre amps. The questions are: 1. how can I make all four XLR inputs simultaneously audible when checking mics for phase shifts, when tracking etc.? Presently, I switch the input on the hifi power amp (one FA-66 inputs to 'CD', the other to 'Tape 1') for either the red or the green units' output, but this only gives me either pair of the four mics, so recording without phasing issues is hit and miss. 2. Is there a routing option I have overlooked? 3. Or can this only be achieved with hardware for mixing? 4. Are there recommended power amps/hifi amps that have more than two inputs that can be heard simultaneously? Thanks for any suggestions!