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.
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.
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.
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.
Yep. If you really get into this, you'll find yourself likely going through quite a few different speakers ultimately! There are so many different tastes, room set ups, personal music preferences, listening habits, and so on, that it's no wonder EVERYBODY ends up with different gear! In all my years around hi-end audio, I've never met two people that share the same systems! I'm sure they exist, but the norm is definitely PERSONAL CHOICE AND DIVERSITY!
My suggestion would be to try what you have already PLANTED in your mind(or you'll always wonder), and then try something else!! You'll never ever know until you walk down the "trial and error" path! Also, play around with speaker placement and differnt seating locations in your room, and learn about acoustics. This will pay HUGE dividends in the end. Otherwise, when you try gear, you wont' know what you got or what's possible with any given gear if you can't set it up right for best sound! This is critical. How big is the room by the way? This makes a SELECTION QUALIFICATION difference.
I could make a TON of suggestions of other chioces depending, but it's way confusing, and you just gotta try some stuff! otherwise, who's word, taste, or recommendations, are you going to chose? We all have our own favorites and personal tastes.
Good luck....try the little B&W DM601's or 602's for the money used, then you'll know what that sound is like. You can always upgrade later.
If you want detail, you will get a ton more of it with Lowthers, than with anything else mentioned here. You may have to make your own enclosure to keep under $1k, but where would you rather have your money, in YOUR drivers, or in someone elses profit margin? Get a pair of Lowther DX2's for $695. Spend the rest on a pair of cabinets. I recommend the Voigt Pipes. Easy to make, even if you are not a woodworker, and cheap for material. There is no crossover, so you don't have to worry about that. Some wood and binding posts are all you need. Good from 40Hz to 20kHz out of one driver. And they look very exotic and cool! Sound will beat anything up to at least $5k.
If you want to see what they look like, click on my "System" link, next to my name below. These are a "quick and dirty" version that was put together for testing, but if you use nice wood, and take your time, they can look very very nice indeed. They are about 6 feet tall. These were made in 1 day. I am not a cabinetmaker. At all. Super easy.
And I thought Twl was going to suggest a Terres turntable. Only kidding Twl :)
I heard the 603S2 ... fantastic rock speakers, but not very subtle. Detail has several forms. One is hearing the smallest sounds, another is imaging.
Based on what I heard you would have to spend more than $1000 new to get the rocking and bass abilities of the 603s with great detail and imaging. Someone above suggested the spendor 3/5 ... with all due respect it's a completely different speaker to the 603, and I suspect anyone who really liked the sound of the 603 would hate the 3/5 unless there was a good subwoofer with it.
So s7horton ... if you like the general sound of the 603, but would like a bit more finess then I'd go a bit higher up the B&W line (e.g. CDM7), but if you'd like an altogether different sound .. more detailed, airy and ethereal then there are many many suggestions.
But, to be honest, the 603s are very enjoyable speakers. you can spend a lot more and get a lot less speaker.
My B&W dealer thinks the 603S3 is godawful! Pretty lumpy bass to me, too. The bargain here is the ungainly-shaped 602S3, by far. For $800 used I bought FAR more natural Spendor SP3/1p, though the B&W will play much louder, deeper, and brighter. Depends what you want. Just stay away from the universally-despised (I just toured Scotland, and ALL the B&W dealers raved about the 601 and 602, and hated the 603...no kidding!).
Maybe it works in your room, though, if the bass integrates in a weird way. Good luck.
The 602s3 is one of the best speakers for the money IMHO but the 603s3 isn't chopped liver! The new 603 (series 3 vs. series 2) has a much tighter defined bass and a more natural midrange than either of the previous incarnations. I think one reason mini monitors are preferred the UK is that the listening rooms are smaller than their US counterparts where the larger floorstanders work much better. My 2 cents.
For lots of clean, rich detail, you might want to look at speakers with unconventional tweeters such as ribbons, Heil drivers, and electrostats. There's a pair of Heil ATM-1 speakers listed here for $600. Note that they like to be out in front of the wall by several feet.