Well, both are solid in their own right, and have plenty of fans here. Can you not try this rig before you buy it? Your opinion is the one that counts, so even if someone has played the 2 together, it won't tell you what you need to know. Only your ears can answer.
"On paper" I don't see why these would sound bad together. The XST is more polite in the upper midrange than the XLT with more low end. I've heard the DB750 through an old school SWR Goliath and it sounded great.
But like Rickenboogie said, you should hear it for yourself.
