L7's do sound like balls....I'm no SQ freak, but I have 2 8L7's and they just sound gay....the whole sqaure sub thing, yeah, technically they have more cone area...but they can lose a lot of ground quickly there with excursion and efficiency.
Honesly, the SX's sound good for you. They get piss loud, sound decent(hell of a lot better then L7's) and in your budget.
SSD's most likely won't get as loud as L7s, Q's probably could much closer though. L7's are loud as subs, it just depends if you like the sound of them or not.