I noticed a couple of these from manufacturers over the years, in theory it ought to serve a few groups:
Folks that may have tried 5.1 and decided that surround / rear channels are not all that...
Folks that have a another two-channel amp to drive the rest of their multi--channel setup and just want the "good stuff" for LCR...
Folks that 5 channels of amplification and want to step up to 11 (in the 2x3 + existing 5 is maybe cheaper than all new 11...)...
Maybe discuss the various scenarios?