I know it doesn't seem obvious a server would make that much difference. Part of it is the quality of the parts. Part of it is the higher processing power and parts selected specifically for audio performance. Servers make a difference more than most people think. Think of it this way. I have had quite a few people order Nucleus's while being skeptical if they actually make a difference. I have never had one returned on my 30 day return policy.
The M1 SE is going to be a bit more detailed than the M3. Soundstage in both cases is huge. I have not sold an M1 and have not heard it. Bricasti said few people ever buy it vs. the M1 SE so I ordered and M1 SE and M3 for my initial samples. The M1 SE is quite a step up from the M3 though the M3 is quite competitive in its price tier.