I can't tell you much about the last 2 amps you mentioned, but I'd bet money the M2 uses the same transistors found in the F5. I'm jamming a lot more power through the same devices Nelson used and they're very reliable. You'll never have problems with that M2, and if you do, the parts are easy to get. I'd call it extremely reliable.
The F5 has a bit more provision for voicing and dialed to it's least distortion figure is cold and analytical. The M2 avoids that with the autoformer gain stage and no feedback. I'm getting a 32 wpc out of my F5 for 92dB/V Focals and it's plenty muscular. You're not going to reduce it to smoke driving it too hard, and it's very doubtful you ever would with your speakers.
The only possible down side with the M2 would be hum. Not all of Nelson's amps are dead quiet and the M2 uses the same transformer and bipolar 24V supply you find in every PP First Watt amp. Usually they're real quiet. Mine, however, has some very mild hum. I did build it myself though, and Nelson arranges his innards differently than I did.
The F5 has a bit more provision for voicing and dialed to it's least distortion figure is cold and analytical. The M2 avoids that with the autoformer gain stage and no feedback. I'm getting a 32 wpc out of my F5 for 92dB/V Focals and it's plenty muscular. You're not going to reduce it to smoke driving it too hard, and it's very doubtful you ever would with your speakers.
The only possible down side with the M2 would be hum. Not all of Nelson's amps are dead quiet and the M2 uses the same transformer and bipolar 24V supply you find in every PP First Watt amp. Usually they're real quiet. Mine, however, has some very mild hum. I did build it myself though, and Nelson arranges his innards differently than I did.