Craig is spot on. Add the sub upgrade. I know what you are saying about running your sub at about 30% gain, which is actually about where most people that are looking for decent QUALITY LFE and bass leave it. It is the people that are just looking for "loud" that turn a subwoofer up. Adding a bigger and better sub doesn't mean that your sub isn't maybe good enough for the sound between say 50Hz to 80Hz, but you will really gain that tactile *feel* (pun intended) with a better sub. Again, not knocking your current sub, it is a very popular model from a good company, but you will get more of an overall upgrade by going M80 with a bigger and better sub than going with just the M100 (which are amazing, but trying to keep you within your budget).
(Case and point about the "30%" thing with the subs. I have a large 4cuft, 12" sub from another company that used to only make subs. The thing it tuned down to 18Hz. I have it in a 14 ft x 24 ft x 8 ft room and have it turned to about 25% of max and can pump out a LOT more clean bass, but... I decided to add a second sub, a sonically identical DIY sub also tuned down to 18Hz for my room because now I am still nowhere near the max of the subwoofer, but also have more air movement and more impact and I love it... I also have 2 subs to even out the bass response in the room, but that is a different story.)
