If you need preamp mode, then you choice should be the 3700/4700. You are right about the headroom room, and I mentioned too, that it is the peaks in music that makes it important to have high power amps. So the first step is to figure out how much "power" (hate that term, but..) you need. There are lots of calculator, I prefer my own spreadsheet based one because it covers more conditions, but the one linked below is good enough.
https://myhometheater.homestead.com/splcalculator.html
If the calculator shows you need 100 W to get 105 dB peak from you mmp, then 300 W is not going to do anything for you. 200 W will get you 3 dB extra headroom that you may never need, unless you listen to 108 dB peaks. And by the way, don't you find 105 dB peak, i.e. reference level too loud, I can even stand 95 dB peak or
75 dB average. So if 95 dB peak is what you need, then even with the calculator say you need 100 W for ref level, you will have at least 10 dB headroom if your need is 10 dB below reference level.
If you look at the 4700's distortions/noise vs power output curve, the Emo amp does not do better. Do a comparison side by side you will see. The Denon does very well in the first couple of watts. Also, yes the first watt, or even the first 0.1 Watt is very important but imo it is highly overrated. Think about is, if your amp is outputting 0.25 W, you are probably getting less than 75 dB spl from 10 ft, then even if THD+N is only -75 dB (that is 75 dB SINAD), the distortions would be at or before 0 dB, would it still bother you, I doubt it. You can ask Amir and I am sure he wll agree, under this condition. Yes, he will tell you 115-120 dB SINAD is needed, but that's under a whole different condition that you may not be subjected to. Damping factor is no longer an issue for most amps any more, that's just another overrated myth. Even Crown audio don't talk much about it any more, that they used to..