I will. For reference, the UXL's 18's are approximately 159.5 sqin, but the new FTW-21's are 254.2 sqin. That's a gain of 94.7 sqin. So in total having the two 21's will have as much radiating area as over 3, 18" UXL's. Another way to look at it is 2, 21" FTW's have as much radiating area as 4 of your S1500 subs. So in total, with 2-LMS Ultras, 2-UXL's, and 2-FTW 21's that would be equivalent in radiating area to approximately 9.4 PSA S1500 subs.
How are you going to fit 10 of those things in your room?