I'm not just saying this because I like SQ subs and amps. I've heard HDS310, 312 as well as CSCStang's HDC310 and Jeff's 18s. They got them to sound pretty good and they were able to make them sound they way the wanted, granted Jeff's setup is SPL focused. I just wanted to make sure we're giving people advice to maximize their current situation before spending more money. If he's not even messed with the HU yet, he def should start there. It's free. You and I both know that you can make a system sound totally different just by adjusting x-over points and EQ. Btw you also know that good sq requires ample power, that's why I asked him what amp he's running.