Ok, so we're talking Aerial 9's. Close, but not quite up to my 10t's. ;-) Ixnay the L-paday. You don't want to mess up what Kelly has done at all. I can guarantee you that those dips you mentioned are room interactions, not the speakers.
It is all about placement and amp control with these upper end Aerials. The 9's aren't quite as tough as the 10t's to site in a room because of the difference in port location but the same rules of thumb apply. Some of this has been covered by other posters.
They need to be at least 5' from the back wall and at least 3' from a side wall. Personally, I would spend the money on the better Aerial speaker stands before I would put any more components in the chain. But that's just me.
The most important issue with getting the most from Aerials is amplifier control. The amp has to have a vice-like grip on the woofers or you get boomy, muddy bass. I would not use less than 250 watts/ch and probably SS.
Another issue is speaker cables. I would not use any of those fat, high capacitance cables. You can hear that in the bass as well. A nice tight thump becomes more like ttthhhhuuuuummmmppppp.
Your room dimensions are similar to mine, except that I also have a L-shape so there is some more volume in my room. Anyway, I found that the 10ts worked best for me on the short wall, firing down the length of the room. This allowed me to get the speakers about 7' from the back wall, and 3 to 4' in from the side walls. From there you can play with moving your seating position but about about 8 to 10' back from a line drawn between the speakers should be close.
