Hi Pete. Which ML's do you have? If they CLS's, not hybrids, look for a pair of Kinergetics SW800 subs towers. Even they guys at ML will tell you that this is the sub system that best integrates with the CLS.
It should, as it (including the crossover) was designed by a CLS owner (Tony Di Chiro) specifically for the CLS's. Hell, they are even the exact same height as the CLS. Like the CLS the SW800's are line sources (to 200 cycles). The results with these subs are nothing short of amazing. However, they are no longer in production and can be hard to come by. But... well worth the effort. After trying other subs I decided to just wait it out and by sheer luck and good timing wound up with Gayle Sander's pair that were just sitting around at ML. Also, after posting a "wanted" ad on Audiogon, I did get a couple of responses. You may try to do the same.
I've listened to Vandy's & REL's in my system and while both are excellent subs they do not work well with full range ML's. If you have hybrids, you are your own as I've had no experience with these and subs. Good luck.