You have a great system. But the answer is:
The B&W 800 speakers.
I own Audio Research Reference 6SE preamp, Reference CD9Se, Reference 160 amps … and in my home theater B&W 805 matrix speakers and B&W 800 series subwoofers.
These are all great components. The Matrix have a specific sound and are ancient.
There are so many astonishing good speakers. But the question is, where do you want to go. What music do you love… what do you like about your current system? There are many more sophisticated speakers on the market today. Your electronics are simply first rate.
Hopefully we can point you in the right direction. Then you can then audition some. Budget? I am guessing $30K to $60K?
I am thinking there are four ways to go:
Hyper detailed / holographic: Magico / Wilson
Natural / musical: Sonus Faber
Rock out: Contemporary B&W
Alternative: Ribbon / Electrostatic.