For what it’s worth, I was able to compare the Mastersound Evolution 845 and the 300B PSE in my system. The Evo845 provided more nuance and effortless presentation. With my 94db passive full range speakers (impedance between 6 and 10ohm) in my 11x14 room, I need to bring the amp volume down to about 10 oclock to keep my preamp in its sweet spot of between 9 and 12 oclock. So in that set-up, the 55W of the Evo845 is definitely a lot more than needed. The 15W rated 300B has enough volume, but not as much refined, which I guess is where the headroom comes into play. I don’t have other data points regarding damping factor however. I had a couple PP amps and a Hybrid /OTL as well, but never achieved as much nuance and musicality as with the Evo845.