I do not know about the XL cables, but I have had TA Ultra with MM and TA Reference w/ MM on loan for couple of weeks in my system (I have very good relations with Transparent dealer).
I got the Ultra first. I was generally impressed with this cable, and liked it a lot. The problem with Ultra is that it is a bit dark sounding, and worst still the treble quality is not up to the generally high standard of this cable. The cheap AudioQuest CV-4 which I use to connect the rear channels in HT has much better resolution than Ultra. I found this distracting and frustrating, since when I pay that much of money for the cable, I would like it to be better than cheap cables in ALL areas, not just some.
After Ultra, I got Reference. This cable was better balanced than Ultra, with more treble energy. Resolution was better, but still - not up to standard set by the cheap CV-4. Other than that - a very fine cable indeed.
After that, mostly for fun, I borrowed AudioQuest Everest speaker cable, which at 12.000$ was twice as expensive as TA Reference. Not that I could afford such an expensive cable, but I just wanted to hear what possible in state-of-the-art design. This cable simply blown me away. It was so much better than TA Reference. I heard definition and resolution that I didn't even know was possible. Simply spectacular. The delicate brush work, the low level detail, the harmonic richness, were all beathtaking. Everest portrayed instruments totaly neutral way, with natural warmth and body - not unlike TA Reference. The bass and soundstaging also exceeded that of TA Reference.
After giving back the Everest I decided to borrow his cheaper sibling - the Kilimanjaro ($6000). This is an almost identical cable in its construction - the only difference is less silver conductors used.
Not suprisingly it also sounds VERY similar to Everest. The same smoothnes, resolution, definition and neutral timbre. I would say that it is 95% of everest, with only difference in less bass slam - not a problem if you ask me. This time it was a fair comparision between TA Reference and Kilimanjaro - both cost 6000$. once again - the AQ was MUCH superior to TA Reference, for the same reason as Everest was. IMO AQ KJ and Everest are both in a totally different league than TA Reference.