Mounting depth should not be a problem with a normal 6-1/2 as long as you use the stock plastic basket. You have to cut out the back to make room for the larger magnet. Do a search and you will find lots of info.

Or if the speaker comes with adapter brackets such as the Focals, Alpines and Polks if memory serves me.

What I mean by "normal" 6-1/2 is no oversize 6-3/4 or 7 speakers. If you want to use them, contact Lucid for their adaptors. Nice design and very simple. Again do a search and also visit the Lucid site. Great info.