Wow! That's a lot of subs.
My only benchmark experiences are with my headphone amp, but I would agree with the general feeling that Benchmark is more about detail and accuracy, while McIntosh is more about midrange and lower treble roll off and liquidity of sound.
I'm more now then ever enjoying amps with warmth and depth and get my details out of my DAC's and tube selection.
So I'd personally go with McIntosh if choosing between just those two, but honestly I think a Parasound JC5 would do it for you.
I absolutely loved that amp and feel it's kinda of a auditory mid ground between those two brands you mentioned.