How do I know what my system's

Your system looks pretty good to me. Nothing jumps out as being obviously inferior or mismatched.

Since you asked for advice, mine would be to identify what you don't like and then use that as a starting point to focus in on where an improvement might be made.

If you're not unhappy with anything invest your money rather than spend it. When you've identified a system deficiency you will then have even more "fun money" available. Spending money with no purpose or goal is more "waste" than "fun".

Sometimes it is not about a particular thing you want to improve, you just need to spend some money and get a new shiny toy, I understand that one. I would suggest the amp and preamp as your first targets. Lots of really nice amps out there right now, I really like the Bel Canto Ref1000's I am running.

Wow, impressed by all the responses.

If the advice is to identify what's "wrong" with my system, well hm. One thing is, once I got it it became really clear which CDs in my collection were sh*t recordings and which were great. So a lot of CDs sorta got relegated. Great recordings (like HDCD) sound great, bad recordings sound lifeless and muddled by comparison. (You know how a CD can sound awesome in your car or on headphones, and then you play it on a revealing system and poof, it's all muddy and congested and harsh. Or is that just me.)

Other than that, I guess I would say I might find it all a tad bright. It does depend on the recording; some are more edgy than others. It might just be a digital sound thing. I play with room acoustics, speaker placement. I'm wondering if a new amp would relax & deepen and such. I dunno. The Bryston seems really neutral, but I know there's more power to be had. I just don't know what more power brings, in terms of the overall tone, exactly. But thanks much for all the replies, and any future ones.

To add one thing (if anybody is still paying attention) I do think my speakers are NOT the weak link, i.e. they have responded a lot to every tweak thus far (cables), and just seem frightfully accurate and responsive, if even a little unforgivingly so in the midrange. I feel I can recommend the Revels for their price range; they exude capability. So there's probably untapped potential there.

Shippack, if I can ask a question of your sub-conscience?
The fact that you ran this thread might suggest that you are just looking for a new sound. To tweak it it somehow.
You sound satisfied with your system and it is a Good system. You own some very respectable equipment. But speaking for myself I am always looking for a tweak here or there to gain or enhance what is already there. Why not look at it as, "where would I gain the most inprovement".
Source, amplification, cableing. I really don't think you can answer that without doing some in home demos of different equipment. That's where I would start. Of course just my own MO.