Thanks for the inputs guys.
Despite getting more recommendations, I think I have to rule out the HSU. Here's my reasoning - feel free to give your input on this too, please.
The HSU is rear ported, and is also 16" deep. I am only looking at about 5" port clearance from the back wall, which happens to be a connecting wall to a neighboring townhouse. These walls aren't exactly well insulated for sound - some I'm thinking having the port pounding so close to that wall is a good way to piss off the neighbors.
Also, the HSU will run me $279.
I can get the Prestige S8 brand new for $251. I know it is also rear ported, but I'll have more like 8" of rear clearance. Do you think this will make enough of a difference to have less reinforcement on that back wall - and therefore less likely to drive the neighbors nuts? Also, this sub will easily fit on the SubdudeHD.
On the other hand, I can get the Chrysalis Starfire 10 brand new for $209. So I'd be getting the best deal with this, and also the longest warranty on the electronics. Not to mention, I'm now looking at a bottom ported (with port firing into the SubdudeHD) and front firing.
I imagine I'd be giving up some performance if I go with the Chrysalis, but I wonder how much relative to the Prestige S8.
Prestige has WAF, better specs (although probably a bit inflated), higher power amp....but is rear ported and has a smaller driver.
Chrysalis is $42 cheaper, has 2 years more on amp warranty, bottom port and larger driver...but is only rated to 32Hz -3dB and has less amp.
So between the Prestige S8 and Chrysalis - thoughts?