Subwoofer budget max $700: new vs used, brand?

Bob is right on. I have the REL mini 108Q and it is great, to 30 Hz. It is a sealed design and is for smaller rooms. I have two Hsu subs, both great and integrate well with music. Your asymmetrical room is an advantage with subs because that may lessen room modes. I just bought a VTF-1 in Rosewood. It is a ported design. It is almost flat to 25 Hz, $550 plus shipping, 30 day return policy, and the finishes are truly beautiful. It is a great consideration. Good luck in your quest!

Bob has a point here. Trying to do both pieces at your budget is definitely a bit of a stretch. However, if I were looking for best performance for the $, I'd probably try to stretch, anyway. Here's why:

Warning: the words "slow" and "fast" are used in the following paragraphs as they are commonly seen on these threads. I'm not saying such characterizations are valid, just commonplace among those with opposing subwoofer philosophies. We'll call these 2 groups A) the "slow is okay" camp and B) the "distorted is okay" camp.

The first focuses on high output & low distortion. These subs are often ported designs. The downside is that such designs are often underdamped and strike some as "slow". The other side usually prefers highly damped subs and looks to sealed designs. These "fast" subs generally produce lots of distortion at low frequencies (relative to the ported designs).

The specs "distortion' and "group delay" (respectively) that reflect these performance paramaters are hotly debated. Each side points out that poor performance on the "other side's spec" is usually inaudible - even if the numbers look pretty awful. My point is that I tend to agree with BOTH sides. My subs perform relatively poorly on both specs, but sound GREAT! My take away is that most well regarded subs of EITHER design probably perform "well enough" on both specs, even if the numbers look ugly.

The further upshoot is that poor performance (and the vast majority of sub set-ups I've heard would qualify as "poor performers" to me) is probably due to something else - like poor integration. My experience bears this out. As my measured frequency response near the x-over improved, the system sounded better. Since I didn't expect this result when I started the experiment (long story there), I tend to put a lot of weight on this result. That's why I'd go controller first.

OTOH, you also have to remember, that you may hear hear things I don't/can't. People hear things differently, one to the next. Just because high distortion at 25hz or lots of group delay is completely inaudible to me, that doesn't mean it's inaudible to everyone! So, beware, YMMV.

One day, I'll replace my subs with better performers. The SVS SB12+ that Bob recommends actually performs pretty well on group delay AND astoundingly well on distortion (talking specs only here!). For the money, I agree that they would appear to represent unusual value and I'll probably do that - even if the measured performance benefits aren't dramatically audible.

In the end, I suspect there's a benefit to owning better performing subs. It's just that I KNOW there's a great benefit to well integrated subs. Hence, my inclination to go controller first. Other thoughtful posters obviously feel somewhat differently.

Marty

A powered James EMB-1000 or possibly an EMB-1200 used would meet your price target. Very musical subs. I would stack either of them up against much more expensive subs than are mentioned in this thread....I had a 1000 now a 1200.

Marty, Bob, Tgrisham, Ghstudio: Great feedback. This is the kind of feedback I needed. I would have take-away information from these exchanges, no matter what my purchase decision. I've used subwoofer's in my sound systems since the mid 80's, and altho I could have intuited the existence of the SMS-1, I was unaware that a reasonably priced device such as this existed. Pointing out that using one could be a priority, is why I talk to you guys.
I gave all your suggestions serious thought and decided to try to get the most woof for my buck in the speaker first, and then followup with the SMS-1 if I can't dial the thing in to my satisfaction. I'm a bit of a tweaker. My son and I spend a fair amount of time "equalizing the room" by ear, each time I change something in my system. If he and I can't get it right, there will be an SMS-1 in my future.
I decided to buy a new Velodyne Dls-5000r that I found at my price point. The fun will come in integrating it.
Honestly, the Legacy monitors sound pretty good alone. If the integration doesn't go well, it's not that long until Christmas :-) And it won't be in the budget to spend much more for a subwoofer any time soon, unless I win the lottery!

REL has a new-ish line of budget subs that you might want to check out.