I guess it comes down to how much bass/LFE you want Bill. I am in the similar boat having a 16x20x8 room that is open to the rest of the basement. I was thinking of getting by with a 350, but really the prices on the HSU or SVS options are similar to the 350, but more in the performance ranges of the EP500.
I dont need the walls shaking, but would like to feel the benefit of the sub in HT movies. The feedback I got from HSU was VTF2.3 minimum, but might want to step up to a STF-3 or VTF3.2 as the extra power would be needed to energize the space. SVS said PB12-NSD, or 20-39-PCi.
I would say if you want bang for the buck, go with HSU or SVS. If you want it to match your speakers, you can settle for the 350, or be more than satasfied with the EP500. The other wildcard that gets good reviews is the Rocket UFW-10 or 12 that looks nice.
This is all the feedback I have gotten with similar requests as yours, good luck with the decision.
