Any opinions on which would be a better sounding optimized Center channel speaker: the Center-XL or SuperSat 60C?

Better for what? They are both excellent center speakers, what's best depends on your system and application.

5.1 Multi Channel Home Theater - combined with Tri-7's , SSAT3 Rear surr.

It depends on:

1) What fits your space;
2) Where you locate the subwoofer(s);
3) Settings allowed on your receiver (single crossover setting or vary by channel);

Here's a simple rule to follow IF both fit your space: If the sub(s) is/are not going to be front and center, the SuperCenter is the prefered choice.