I'd worry a bit about the dip to 4 ohms min impedance. But I also second the recommendation of checking with Ralph. It may be that buying the Speltz Zeros would be a good move with those speakers and the M60.
Atma-Sphere MA60's with Proac Speakers
I'd like to know if anyone has tried this combination. I'm in the market for good tube monoblocks to match with my Studio 140s.any other insights/recommendations would be welcome. I've spent the last long while working on room and have got out about as much as I can with my gear.