^^^ there are two main methods to calibrate levels for multiple subs: gain matching and level matching. Both are simple procedures and not much more complicated than setting the proper level for one, which you will have to do regardless. The miniDSP will provide low frequency EQ beyond Audyssey's ability and timing flexibility. Timing flexibility being more important if you only have one sub out and have two or more subs positioned in non equidistant locations.
Which method is right for your situation will largely depend upon where you place them in your room relative to your main listening position. The point of having more than one sub is not to blow your neighbors out with added SPL, but to even out the response across the room. When done right, this actually minimizes the mad neighbor affect. Counter intuitive I know, but peaks and nulls (often associated with one sub) are a bigger problem for the owner and his neighbors. i.e. you're sitting in a null, so you crank it up on certain tracks/movies, but your neighbor is sitting in a peak. Next thing you know, you have a Cop Knock at your door and you're wondering if it was a real knock or if it is from the movie you're watching.
With your budget and usage, I would only consider a single sub if I was sure I could not fit another with some flexibility for placement. If you do determine one is indeed the only option, then that L22 from Rythmik is a top choice. Assuming you want to stay sealed.
I know musical fidelity is your top priority despite usage percentage, but Rythmik ported models are generally considered to be as "musical" as everyone else's sealed models. Kind of a best of both worlds. Question: when listening to music, will you be sitting in the sweet spot, or moving around and expecting a balanced sound?
As far as bag for buck, SVS generally ranks last amongst the ID sub mfgrs. Their key benefit is their return & upgrade policy/Customer Bill of Rights which you will pay a premium for upfront. This may or may not have value to you. You'll have to be the judge on that but Rythmik has top notch support in addition to other customer loyalties. PSA & HSU also enjoy great customer loyalty due to their product performance and customer support philosophies as well.
I would rule out Rel and ML.
If you have not done so already, I would highly recommend you read through this https://www.avsforum.com/forum/113-s...rences.html#II
The whole guide is well worth the investment of time, but if you want to skip to level calibration that should be the right link, I think.