2- At the moment I don't use class d on horns, although when I did I was surprised. The top end was the only part that really didn't sit well with me. There are much better class d amps than the Behringer. It is better suited to lower frequencies.
3. The 2226 only uses 1 coil in the crossover. Modifying the crossover for Bi-amping would be easy enough to diy. Level matching is quite easy when the amp has gain controls. One could probably lift the crossover padding on the horns since they don't need to be padded down to the 2226's level. My 2a3 amps would like this!
4. I have a serious sub in the system now but I still feel that 2226 came to life with class d enough to justify another amp.
5. Sub is being moved around the room while I take measurements. It is a work in progress. I can't locate it, if I keep it under 80hz no matter where it goes.
Once I dial in everything under 300hz, I will start looking at the rest of the system for possible improvement. I guess you could say I'm take a "bottom up" approach.