Audio Research, next upgrade?

I don't think upgrading to the MKIII version is going to buy you anything. You may want to consider a VS115. It uses the KT-120 as well as 6H30's. You would get greater dynamic range, and speed. I don't think you would loose much if anything in the way of bottom end slam either. See if you can borrow one to try. You may be very surprised.

I had an LS 26, and compared to what it replaced (a bottom of the line VTL tube pre), the low bass was anemic. You have good bass in your speakers and amp, so if you like low end extension and weight, replace the preamp. I went SS to match my amp, and the difference was immediate. I miss the sweetness of tubes, though, so want to find a tube preamp that can go low. LS 27, 5 SE, or?

I am very biased first of all so take all of this with a grain of salt. I am also the maker of the VERITAS Monoblocks.
1. Keep the pre.
2. For you 87db 801, switch out to VERITAS monoblocks - based on other users with 802, MBL's etc. I have compared the VTM 200 to the VERITAS in many systems, is the VERITAS make a large difference. It has not been compared with the VTM 100, on 801 do this is an assumption that it would be better since it was done with VTM200 monoblocks and 802's.
3. Move to Computer Audio with a good DAC - Phasure is excellent however a good DAC with 24/192 will let you hear the emotion in the music. The CD player is good, however once you hear excellent recordings without the missing bits/jitter and other CD associated issues, you will understand.

Good luck!