Attention to detail

If you want gobs of detail in that price range I would recommend the Martin Logan Aerius (i--if you can get it for <$1000). You will sacrifice some of the bass you've gotten from your 603s, but you will gain a tremendous amount of detail, air, and transparency. If you have not listened to Martin Logan's you should to see if they are the right type of speaker for you--they are not for everyone--and speaker placement is very critical.

You may be able to find a used pair of Merlin TSM monitors in that price range. The Merlin speakers are very detailed, yet still very musical.

Are you sure you have the source and amplification for your priority? I am not implying you don't, but one has to really like the what the upstream does when they want to hear all of it.

Check out the Totem speaker line. The Arros are $1100 new, the Rokk, and the Mite are close to that price also. I have the Arros and the Model 1's in 2 different systems and enjoy them both.

Spendor S3/5 for $600 used...or better the Spendor S3/1p for $8-900 used: +4dB more efficient, with much deeper bass.
I just built an entry-level system for a good friend from these Spendors and a used Complete Integrated, fed by the new NAD 541i CDP through Nordost Blue Heaven to start.
Should turn out exceptionally well, I trust. The lushness of the ARC and the exceptional coherence of the Spendors should seduce.