"Fact is it's a tough combination to beat no matter what your budget is."
Reading back over this. Another thought along the same lines of thinking...
Yep, levarage the existing amp as-is, keep it for a few more years, at least. Having owned the BF 2/64 myself, its an ok DAC for the money - yet more to be gained with a 1 or 2 level up dac for sure if you are looking for more lush velvet and musical sound. Some dacs are "overly precise", too analytical for me, or imo.
A really good DAC, nice Digi Coax cable, nice output interconnects to the PA-7 II, and you'll hear the existing amp and Acoustats in a new way. Demo 3-4 more dacs first. Try this for a while, might be pleasantly surprised.
Then, after this is set up well, IF the new-amp-itch is still there for a set of "monos", start demoing (buy/return/keep) and comparing decent monos to see who can dethrone the recently refreshed PA-7 II. Would not be suprised if it holds its own.