I have had great sucess with Musical Fidelity and B&W 800 series. I have an A308CR preamp and Bryston 7b ST monoblocks. The MF A308 has a "tubelike" top end that works very well with nautilus tweeters. I have heard many say that Nautilus tweeters and Bryston amps are harsh. I have never had this problem with N801's nor with S800's.
You can go the same route with a Musical Fidelity pre like an A308, A3.5 or A3.2 pre(I also have a CD Pre 24 in my office - awesome unit, Preamp, CD and DAC/ADC in one box) and a Bryston 4Bst amp if you don't mind going separate.
If you can find a MF A308CR integrated, it should be below your budget. The A308 is teh last to be made in England and supposed to be extremely reliable.