signal as well as possible. So, I have two heads. Both have effects loops. Here is what I want to do... Each loop "send" goes to this mixer. The signal from the mixer goes to the "return" of each amp. Each amp is powering it's own cab. My intention is to access each preamp as needed and utilize both power sections at all times. I can utilize the "Aux out" on the board and drive effects which will go to their own channel and be manipulated as I see fit. My guitar is going to an A/B box so I can switch to each preamp as needed. I am going to run this to one of my smaller mixing boards to get the bugs worked out, but.. I want to purchase whatever unit will handle this mixing task, yet preserve the guitar/amp signal as best as possible. What unit should I check out?