Agree with
@lovinthehd, get a better sub. I had SM55s when I first started posting here and they're not bad speakers. You get a good sub in the mix and you can have a pretty nice sounding system. I've had 2 big "wow!" moments when I started upgrading. The first was my subs. I went from a pair similar to yours to a pair of
VTF 3 MK5s. It wasn't what I expected. I expected deeper bass for sure, which I got, but it was also much cleaner. In fact, my new 15" subs seemed to actually sound quieter than the old 10" subs they replaced. At first I was a little confused, then I realized what I was missing in volume was the distortion. A good sub can help clean up your sound across the board. Who'da thunk?! True story tho, good subwoofage is often underrated. I was genuinely surprised.
If you were to upgrade your front speakers I'd suggest moving out of the deftech family and look at some other brands such as SVS, Salk, Ascend, RBH... as I'm typing I'm realizing there are too many to list, lol. If you stay with bookshelf speakers instead of towers you can get better quality parts and build for the same money. That was my second "wow!" moment. I bought a pair of
SVS Ultra bookshelf speakers from their outlet for $399 apiece (where that links leads to) in piano black gloss after some research and suggestions from here. They're a clear step above the SM55s across the board (again, the 55 isn't a bad speaker, but you pay more for the Ultras too). I loved them so much I ended up getting the towers and moved the bookshelves to surround duty.
But I digress... upgrade that sub! I think you'll be surprised like I was and you might end up hanging onto your 55s a little longer. A good sub integrated properly with a good set of bookshelf speakers will sound great and play lower than many towers will.