I've never had "XL" speaker cables. I had Transparent Super (the original) in the big system for my Maggies, upgraded to Ultra MM, then upgraded to Reference BiCable (MM) for the Vandersteens.
One thing to keep in mind is that "XL Technology" wasn't really technology in the form of circuitry or hardware; "XL Technology" came about because Transparent got some exotic test equipment to use with their high-end cable (which became "Reference XL," as opposed to the less-lofty "Reference with XL"). They started using the exotic test equipment on a big chunk of their cable line, improving tolerances and consistency. That's why the cables got the "XL" stamp.
MM is a true upgrade, in that it's an actual improvement in the design and materials.
