Used Sonus Faber Concerto or Concertino.
I love my Von Schweikert VR-1s. Lowest frequencies are flat to 60 Hz (-1 dB) and 40-50 Hz in room. Great midrange. I use them in my library mainly for small classical and jazz. They are beautifully finished. Used here on Audiogon would be a good bargain, in the $600 range, or new on-line for $995. There are many, many monitors in that range that are wonderful. It will come down to personal taste. Good luck.
I've been thinking of upgrading my 10-year-old B&W 805s (pre-nautilus). I paid over $2K but would sell for $1k or so. I think they're quite musical and warm, and the imaging is great. They don't suffer from the brightness that some people attribute to the newer B&W tweeters. They're not terribly efficient, though, and I don't know the power of your amp. My 85-watt Creek integrated is more than powerful enough for my moderately sized room and moderate listening levels.
In a lower price category, I recently checked out the Wharfedale Diamond 9.1 for a friend. $350/pair. I was most impressed with the sound quality at that price.
Vienna Acoustics Haydns. I have had a pair in my office with even an
adcom amp for over 8 years and have never really gotten the itch to mess with them, very very musical, not picky about amplification. When I changed the adcom for a bow wazoo and an old rega planet< i got true minimonitor heaven for cheap:)
If you've got room for floorstanders try the Jamo D450's, I currently run them with the EE M520...I also have used Reference 3A de Capo i's ($1k-1400 used) and an older speaker, if you can find them are Dayton Wright LCM-1's (probably $600-700 used).
The M520 is quite an integrated (even better if you can put a preamp in front of it) once you get ride of the Chinese tubes...I've been living with one for almost 2 years now (in the main listening room) and I haven't had one last anywhere near that long previously. The only integrated that I've tried that even comes close to it is the Nelson Image 66i which uses KT-66's, but doesn't have a remote option or tape out, so the wife nixes its use in the main room.
Good luck, and take your time, the journey is part of the fun with speakers.