Passive sub for Magnepan 3.6r?

Intrigued by the fanatical praise for the Magnepan line, my buddies and I finally got the chance to audition same at length. The 1.6s were fairly engaging, though a bit bright to my ears, and wholly lacking in low end slam--overall there's a number of conventional dynamic speakers I'd choose for the same $$. The 3.6rs, however, truly are as awesome as their cult proclaims--they reproduce drums and vocals as well as anything I've heard and are incredibly transparent. We did an A/B comparison of the Maggies to comparably or higher-prices B&W Nautilus and Thiel floorstanders, and it was absolutely no contest--next to the Maggies, the others sounded veiled and boomy.
All that said, and with due respect to those that enjoy the 3.6rs w/o a sub, we all felt that the 3.6rs lacked bottom end impact and were, in effect, 80% of a great speaker. We then added a REL sub (as is often recommended), but still struggled with the integration--no matter how we adjusted the sub, the combo still sounded like two separate speakers, not an integrated whole.
So my question is, assuming I take the plunge, would the Maggies be better served by pairing with a passive sub? My concept, as yet untested, is that by using the same amp to power both the sub and the Maggies, I might get a less distorted, more seamless sound. While I'm sure this topic has been addressed somewhere, your informed opinions would be most appreciated.