I'd go for a either a MOSFET/tube hybrid, a 50 wpc Class A SS amp or a strong tube amp. I've run my N804s with a couple of 16 wpc 300B SET amps and a Sugden Au51P power amp, and they just sing. A used push-pull tube amp mated with a passive line stage might be just the ticket.
B&W 804 with ???
In the midst of upgrading system. 804's are new as is Rega Planet; these are currently driven by an old Hafler and Acurus L10. I listen mostly to Rock, Jazz and have some interst in decreasing the brightness of the 804's a bit. Integrated, separates, just the amp, just the preamp ?? would like to keep cost < $2k. Thanks !