Thank you - that's quite helpful. The MRX 540 is new, and while it does have pre-outs for all channels so I could absolutely get a more powerful 2-channel amp down the line, it's not in the cards for the short term.
My current space is about 15'x17' with 8' ceilings, I generally listen with the amp at -35 to -55 (I haven't measured actual volume level). I primarily listen to Rock (Phish, Grateful Dead, Radiohead, King Gizzard, Pink Floyd), but these will also be for home theater use.
But this is making me think Salks may be more appropriate as they seem to be happy with closer to 100wpc and I don't plan on getting more power for quite a while.