How do I know what my system's

From my own experience, every system has its weak and strong points. You must know what your weaknesses are then you could upgrade from there. Without listeing to your system there is no way anybody could tell you what to do. On the other hand, if you got to buy something I would go with new speakers. They usually make the most immediate impact.
Nick

A good approach to this is to ask yourself some questions:

What does my system sound like?
What do I like about the sound?
What bothers me about the sound?

You need to know what your goals are with your stereo system. It takes time, trial and error, and experience with different systems to figure this out, but it's the only way to upgrade sensibly.

Recordings recommended by people on the web, audio reviewers, and friends can also help get an objective handle on what your system sounds like. These especially help if you have others' descriptions of these recordings sonic qualities to calibrate both your own experience & descriptions and your system's ability to replicate these qualities. I don't know enough about CDs to recommend anything here, but I assume there are such lists available online.

Another useful tool is other people's descriptions of components in reviews and discussions. Certain products and product lines have consistent qualities and reputations. Use these to figure out how to change your system's 'negative' qualities--the answer to the third question above.

These are generic suggestions, so please forgive if I'm being too basic, but I think finding a clear and coherent set of audio goals--and figuring out how to achieve them--is a huge hurdle in this hobby. After that, reading reviews and making upgrade decisions gets much easier.

Good luck!

You could buy a pretty nice iPod for a couple thousand! Just kidding. However, I did notice a lack of analog. You could add a nice TT and phono stage. Otherwise, I'd keep it like it is and buy music or go see some live. A couple thousand...eat, drink and be merry.

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.