I've owned P/Es for over 10 years. A few observations, FWIW:
IMHO, this is a very fine speaker, but there is a noticeable hump in the octave below 100hz (exactly where is room dependent) and gently falling FR thru the mids and treble region - with the exception of a "plateau" thru the presence region that probably contributes to the speaker's striking dynamic impact. I suspect that the overall falling FR is why some say "dark" while others say "musical". For any given listener, that distinction might well end up being source, room, and system dependent.
Close to wall placement may further emphasize the bloom in the bass, so I'd personally suggest that you get 'em away from the boundaries. Also, warmer sounding tube amps can be problematic, per several posts above. I agree that ARC works well, as does quality solid state amplification.
This is a moderately tough load, so low output SETs and OTLs need not apply. I'd also note that there's limited bottom octave output with any amp, so real bass freaks can probably do better for the $.
If you get all the other stuff (room, system, etc) right, and you don't need the pipe organ / HT option, IME the P/E sounds really, really good with a broader range of source material than most other speakers that I know.
Marty