I have the REL Q150E, currently using it with B&W 685s as fronts, HTM62 centre and M1 rears. It works fine with this setup, but it is a leftover from my old system and I am intending to replace it. The 685s are obviously pretty good speakers when it comes to bass so I honestly don't know if it will be a shortfall when it comes to using M1s all rouund. It's not huge though, so I'd take it with you to somewhere selling the M1s (and even the KEF / Quad packages) and demo it.
EDIT - sorry, just realised I gave you very similar advice in another thread!