Originally Posted by movieman_78
...my feeling is that the Klipsch had a very good sound at first impression. I quite liked the crisp highs and I loved the deep lows. However, I felt that it had absolutely no middle range and am worried that in my small room the highs will be too overwhelming. The Mythos on the other hand, had a great all-around sound and although they weren't as crisp in the upper registers, I heard quite a bit more detail. I just loved the range in them, not nearly as stark as the Klipsch.
... I found the DefTech subs to be lacking impact and going with the Mythos would limit my sub budget. It seemed like the Klipsch sub had more bang for the buck (pun kind of intended)...
Many speakers are impressive in the showroom, but become fatiguing in long term listening. The Mythos give a balanced response that doesn't overly emphasize any part of the sound spectrum, and thus are satisfying to live with over long periods.
Similarly, some subs impress by emphasizing mid-bass frequencies, but begin to sound "boomy" with extended listening. As surma884 said, listen to some high quality subs in a good listening environment. You may not be able to afford them, but you will get an idea what to listen for. You may find they "lack impact" initially, but provide accurate, extended bass that is more satisfying in the long run.
The Klipsch Sub-12 certainly has its fans, but there is a lot of competition in that price range. DefTech makes fine subs, but the "best bang for the buck" in subs tend to be from ID sellers, and there are some excellent options available from the likes of SVS, Hsu, Outlaw Audio, AV123 among others. (Check out the sale on Outlaw's well regarded LFM-1 Compact, which seems like a great fit for your situation, both in size and price.)
In any case, to answer your basic question, you can use any good quality sub with the Mythos.