If running my 990 into a Crown XLS 202 do I need to put something in between them to match the levels?

You shouldn't. If you are worried about matching the left and right channels' levels, the 990 has internal adjustments for that as well as test tones to help with calibration.

And use the 990's balanced outputs. The crown is expecting pro audio level inputs. If you don't have any XLR cables, bluejeans cables makes some very decent ones pretty inexpensively.

edit: As does Outlaw, I belatedly note.