I have a stadium II hooked up to two Cary Slam-100's and there's no problem. Some posters have said that two subs are better than one - and I have no reason to not believe them - but if you don't have sub set overly high and you're not sitting right next to it, low bass waves are remarkably non-directional and it won't sound like the lows are coming from the sub at all.
Start with one, see how you like it!
Start with one, see how you like it!