That's not a "pre-amp", it is a power amp.

I'm guessing that you're using the 805 as the pre-amp, and feeding the pre-out signal to the AudioSource amp.

Could be a connection issue.

I would not fault the M60's. I would not cross them over at 100Hz.

I'm skeptical that these amps would provide a meaningful improvement over the internal amps of the 805.

bibere usque ad hilaritatem