Manley with Harbeth Monitor 40.1

I've not tried Manley with my 40.1's, but can recommend Music Reference RM9 MKII, McIntosh MC275 MKV, VAC Phi 200 and VAC Renaissance amps.   All slightly different flavors, but the best all-arounder of the bunch is the Music Reference RM9 MKII.   

If you tell me what genre's of music you prefer and the sound qualities you value most, I may be able to steer you in the right direction.

Regafan, in my many years of owning 40.1's with a variety of amps I have not found it to be an absolute that the speakers require high power.  I'm currently using 70 watt per channel VAC 30/70 Signature monoblocks that drive them effortlessly and I also drove them successfully for two years with a McIntosh MC275 MKV.