What mixes with Transparent Ultra Xl Speaker Cable

Do what Cytocycle suggests. Transparent's recommendation is that it's better to have a high-quality single cable with jumpers than use lesser cables for bi-wire. My previous experience has borne this out.

OTOH, if you can afford to go the Bi-Cable route at or above the level you're at now (i.e. Ultra w/XL or better), do it.

Bwyoung, Transparent strongly recommends AGAINST using two separate cables for bi-wiring as you suggest. They say the networks can interact in unpredictable ways and affect the sound.

At one point I tried a bi-wire with MW Super on the top and MW on the bottom on some Maggie 3.5s; found that the sound was better with just the Super and jumpers.