Of the speakers mentioned, I like the Amphion suggestion. PMC also has some nice monitors and are, to me at least, a cleaner and more refined version of Amphion.
The Sonner Audio Legato is another candidate with an open/airy sound and some warmth sprinkled in.
As a Harbeth dealer I have a love/hate relationship with the P3ESR. It is great for what it is, but also has some physical limitations leaving me to ask many questions to verify my clients would be happy with it. I think the Monitor 30.1 would fall more in line with your expectations due to their richer tone and deeper bass.
My personal recommendation though would be the Rosso Fiorentino Pienza. It's a ridiculously large sounding monitor that has never failed to drop jaws when I demo. There isn't much information out as we are awaiting the second generation to be released, but that should happen in very short order. Rosso in general reminds me of Magnepan in the way it reproduces the music, but it also gives you the energy of a dynamic speaker.
Disclaimer - I am a dealer/distributor, but have no affiliation with Amphion or PMC.
I should add that Fritz speakers do remarkably well with low-powered tube amps. My recommendation is based on hearing them powered by a Modwright SET headphone amp. See also this thread:
I have Spendor D1 and Rel R-328, at combined msrp of 5k but less than that used, and they are really good.
Spendor D series have a faster, more modern sound than classic Spendor (I also have SA1), and I suspect Harbeth (can’t say for sure Re Harbeth as I have not owned). It’s personal preference of course but If you can find D1’s, they might fit the bill