ShinyChrome:
There is a SVS PB-1000 on TradeMe for a decent price at the moment that you might consider with any leftover budget. Q150/S15 + a PB-1000 would be a killer budget setup.
Managed to save $500 today on a couch today after a great deal on FB, so may be able to get the sub after all.
The SVS PB-1000 looks great but sadly I'm in Hamilton, sister's going to Wellington and back in Jan but can't imagine they'll still be around by then.
There's a JAMO J-10 Active Subwoofer on Trademe for $400 new, but I can't find much out about them online. Seems to sell for ~600/700 new but googling also showed me Newegg has sold then at $100 before- which was just another depressing reminder that living in the US occasionally has its benefits.
Any other suggestions? Not really looking to spend past $500 unless it's a bargain (like the SVS PB 1000).