Pity you need the information now rather than in a couple days when I could give you some feedback on part of the issue. I have the 604S3s and LCR60 centers (I run one above and below the screen). They were sort of temporary when I got them, and I'm just now upgrading to the HTM 61s which are a large leap up in design/freq response at least.
I expect them to still be a pretty good match with the 604s, or I wouldn't be doing it. Until I get them home, hopefully on Monday when the store gets them in, I can't tell you if the match changed from what I've got now. That is a good price on the 604s...
The one other thing is the unfortunate mismatch of the fronts of the two speaker series. If you have the grills on it wouldn't be so bad, but I like having mine off. It's worse since I have the oak finish.
As far as my own opinion of the 604s so far, with nothing really to compare them to, there are certain times they could have maybe used a bit more cabinet bracing. Instruments in the mid-bass frequencies such as timpani seem to have just a bit of extra resonance. I don't know if they changed that in the new series, but you might ask. Other than that, and it's not bad, I love them. I wouldn't want to go smaller if I didn't need to for some reason.