I'll start off disclosing I have not heard an 802 Nautilus, but I have heard 802D and own 804S. I suspect the latter shares the aluminum tweeter with the Nautilus.
I think tubes and the aluminum tweeter have a lot of synergy. I drive my 804S with McIntosh MC275 and love it.
However, the 802 needs more power. I know people using MC275 as monoblocks to drive 802D. While that's an option that could be within your budget if purchased used, you need to factor the cost tubes over time. Remember you will need to replace tubes...and when you get into rolling you will be talking a lot of tubes! So I don't really recommend this option, but suggest you audition a MC275 and 802D and 803S combo to get a flavor of tubed amp and aluminum tweeter.
On the solid state side, McIntosh, Classe, and Rowland (model 4/6/8/etc) are generally very well liked with B&W. On the McIntosh side you probably want a 402 at least. With the 804S I preferred the 275 over the 252, despite the latter having a lot more power. Amount of power is not everything!
On preamps I can't help but recommending tubes. Whitin your price range you have many options and you need to think what is really critical to you. Sound itself, remote, balanced design, XLR connections, integrated phono stage, input gain matching (to compensate for different sources supplying different voltage inputs...so you switch source and you listen at the same level...I guess important to some). I have recently gone through a preamp search, so I'll tell you my take on the ones I looked into. They all sound very good, by the way. My point is at a given price point it's a tradeoff between sound a aesthetics and bells and whistles:
- McIntosh C2300: beautiful looking, lots of bells and whistles, RCA & XLR but not really a balanced design, phono stage, remote. C220 fits all the same, but less than C2300. C2200 is earlier version and very good too.
- Aesthetix Calypso: nice looking, remote, balanced design, XLR & RCA, no phono.
- Audio Valve Eklipse: very nice, remote, no phono, can't remember if it had XLR. I really like this one.
- Joule Electra LA150: some like the styling a lot. To me it's not a high point. Remote, optional phono, can't remember connectors. Quite a tuby sound (aka, less neutral than others).
- Herron VTSP2: nice looking, remote, no phono, phase switch. Very nice. VTSP3 is said to be superb.
- AtmaSphere MP3: not ugly, but its aesthetics aren't a high point for me. No remote, optional phono, balanced design and XLR only. I liked this one a lot but my source didn't have XLR.
- First Sound Presence: not ugly, but its aesthetics aren't a high point for me. No remote, no phono, two volume pots, RCA only. Mr Go, owner and designer, only makes preamps and believes XLR has no advantage over RCA for typical domestic applications. He has very, very expensive preamps (4 boxes!) that only have RCAs. This preamp is a hot rod. 100% of budget spent on how it sounds, in my view. I came this close to buying it.
- Lamm LL2 Deluxe: This is what I purchased. The ugliest of the pack! Another hot rod, 100% focused on how it sounds: no remote, no phono, no input matching, 2 volume pots, RCAs only. So you know where my preferences make me lean to.
Needless to say try and audition if you can.
Source: I also have Rotel, but RCD1072. My next upgrade will be a DAC. Maybe Bel Canto DAC3, Bryston, Weiss DAC2, or Wyred4Sound DAC2, and use the Rotel as source and later a computer. Digital is still changing fast.
Sorry for the ridiculously long answer. My longest post ever. I promise it won't happen again!!
