Mono is almost always better with the AHB2, except with my hard to drive Thiel CS3.7. The stereo amp is actually better suited than the mono since it can go down to 2 Ohm area. I now use the AHB2 with KEF LS50's but once I get a more AHB2 suitable speaker, I will re-buy the second AHB2 that I sold.
The AHB2 becomes quieter, plays louder, and stronger in mono. I know from prior experience with other speakers.
I also do not buy expensive interconnects to hook up the AHB2 since it is AES48 compliant. I use 15-foot Benchmark XLR's. The AHB2 benefits from good speaker cable. I use Audience FrontRow with SpeakON termination at the amp end. You can also use short cables when you go monos and use the cheaper XLRs for the longer lengths to the AHB2s from the preamp,
The AHB2 is my favorite amp though I have others that cost much more.