What should I upgrade next?

Should your room be tweaked to your satisfaction than the speakers would be my next concern. When you begin to hear what your don't hear so to speak, it may be time to upgrade your speakers. Beyond that it may be that expanding your system into a computer based or media server component will bring more joy and more use of a already fine system.

At the time B&W wanted to shift (rise) the price of the big 800 series and they managed to justify by building a new tweeter. (this gave a +50% price rise).

I would keep the speakers, the diamond tweeter does not worth the difference.

on the other hand i would do something with the sources. I am a TT fan but since you prefer digital i would buy a DAC and rip my cd's in flac format. try downloading a couple of hi res tracks and you will hear the difference.

make that a DSD capable dac, plenty starting at relatively low prices

I recently spotted an ad for Audiopoints that fit B&W here on Audiogon. We had vintage 801 Matrix III’s in the studio for some time and found that adding these devices led to a much more musical outcome. These brass cones worked beyond our expectations so we decided to hold on to the monitors. If you are happy with the 802’s then in my opinion I would upgrade them. The increase in speaker performance is well worth the price of the points.

I would also follow up with LAK’s advice and work on cleaner power, isolation transformers, AC distribution or better racking prior to room treatments.

What specifically is missing from the sound of your system? It appears that your system is very nice indeed. I agree that room tweaking is very important. Also, you may want to borrow a nice DAC to see if that makes an appreciable difference in sound (it definitely will) before tweaking too much or buying anything.

Always demo in your system before purchasing.

enjoy

I agree with those suggesting tweaking the room acoustics to include a reevaluation of speaker placement, listening position, and equipment placement.

I also agree that computer audio would be a nice fit.