I have 170's as surrounds in a 5.1 system and an HSU VTF3-MkII. I can't compare it to any other internet direct subs, as I haven't heard any others, but the HSU has not left me disappointed. You can also get good package prices from Ascend.
Rob... Depending on the price range, take a look at the STF-1, too. For music, I actually thought it did a great job with the 170's. Solid bass to 32 Hz... and very tight and tuneful, as the Brits would say.