I like the 603 better than the 604 as well. The bass was better controlled IMO. They both sounded a bit boomy to my ears. The 683 improved the bass, but messed up some other stuff IMO. Its all a trade off. The uncohesiveness I've heard in them wasn't due to electronics or the rooms. I've heard them with Mac, Bryston, Rotel, and NAD gear. Same results every time. Everyone's ears are different.
Regardless of this issue, I think going from 603s to 683s is more or less a lateral move. Perhaps a little better, but not a night and day difference in the end. I think it'll be more of a change than a true upgrade. If you're after significantly more bass energy, I doubt the 683 will be much of an upgrade.
If bass is your problem, have you tried playing around with placement? Improper placement can cause a ton of problems, most notably bass issues. There's no one correct way to place a pair of speakers, and a lot of it is trial and error. Here's a link to a great placement article if you're unsure about it -
http://www.audiophysic.com/aufstellung/beispiel_e.html
Also, what does the rest of your system consist of?
If that's not the problem, an excellent speaker I heard are the Revel Concerta F12 for about $1500. They've got a ton of bass and sound great too. I heard them next to the 683s and there was no contest to my ears. There was nothing the 683 did that the F12s didn't do far better. If you need low end slam and punch, these are a must audition IMO. I really liked them, but my room is way too small for them.
Just my opinions. Take them as you will.
JR
Regardless of this issue, I think going from 603s to 683s is more or less a lateral move. Perhaps a little better, but not a night and day difference in the end. I think it'll be more of a change than a true upgrade. If you're after significantly more bass energy, I doubt the 683 will be much of an upgrade.
If bass is your problem, have you tried playing around with placement? Improper placement can cause a ton of problems, most notably bass issues. There's no one correct way to place a pair of speakers, and a lot of it is trial and error. Here's a link to a great placement article if you're unsure about it -
http://www.audiophysic.com/aufstellung/beispiel_e.html
Also, what does the rest of your system consist of?
If that's not the problem, an excellent speaker I heard are the Revel Concerta F12 for about $1500. They've got a ton of bass and sound great too. I heard them next to the 683s and there was no contest to my ears. There was nothing the 683 did that the F12s didn't do far better. If you need low end slam and punch, these are a must audition IMO. I really liked them, but my room is way too small for them.
Just my opinions. Take them as you will.
JR