2 channel setup - Should I add a center channel or $1500 subwoofer?

Better off with four $350 subs. IF you have the space. Unless you prefer lower Hz in one listening spot.

^^^^THIS!^^^^

Nothing beats 4 subs! Other than of course four even better subs! But four small ones is WAY better than one of ANY price or power!

Unless you have people sitting well off center (in front of one of your L/R speakers and beyond) I’d definitely go with a sub as it adds so much more to involvement and the whole movie experience.  SVS is fine and offer good service and value.  Enjoy, and best of luck. 

As said above, the center channel is mainly for voice, so if you can hear dialogue clearly already, then as most others say, get the Sub(s). Also, the center channel will in my opinion make 2 channel music sound worse. I spent plenty of time and money on a high-end HT system and 2 channel music never sounded anywhere as good as my 2 channel.

The only person that would benefit from a $1500 sub is the guy who sells it to you.

This is an interesting thread that I missed the first time around.  I would have done both, perhaps buying used, or if new spend about $1K for the center channel because I do think it enhances dialogue and get a small sub for $500, and then upgrade as funds allow.  I wonder what the OP eventually did