Need a new subwoofer for music > HT in main room

Room is 24' x 15' with an opening for 2 hallways at one end. 9' ceilings.
NAD T760 powering Monitor Audio Silver 7i with Gold Center, no rears.
Room is far from empty (plenty of sound damping). Hardwood floors.
Currently have an old M&K 8" sub that should be relegated to less-demanding work - honestly it's fine for music - I just noticed it get a little unhappy recently during a movie, and later with some loud music. I need a little more, but not a TON. I do not want a situation where the bass carries throughout the house far exceeding the carry of the MA speakers.
Since I listen to mostly music and don't care about the whole extreme-home-theater bass-shaking experience so much, I'm thinking about the following subs:

• SVS SB-2000
• Hsu ULS-15 MK2
• Rythmik F12-300

I was originally thinking about something from Monitor Audio (W12?), but from some reading it sounds like I can get a better sub for the same $$$, or as good of a sub for less $$$ (latter preferred).
There are a couple on the classifieds that caught my eye, but I know nothing about them.
Would appreciate being able to save $$$ and buying used if the sub meets my needs. Options include:

• Axiom Audio EP500 v3 $375
• NHT B-12d $395
• NHT CS-10 $325
• REL Acoustics R-205 $350

TIA!