I know it's big, but I'm not sure if it qualifies as "too big": PSA XV15
- 15" driver
- 500W RMS amp
- 21-200Hz +/-3dB (16Hz-18Hz typical in-room extension)
- 23.5" (d) x 18.5” (w) x 24.25" (h)
You'll get excellent output and extension, and it's reported to be just as good with music as it is with movies.
Re. your list of subs:
- The Emotiva X-Ref 12 reportedly rolls off fairly quickly below 30Hz. Great sub for music, not so much for movies.
- The REL T7 (200W RMS, 30Hz @ -6dB) and REL T5 (125W RMS, 32Hz @ -6dB). Meh.
- Def Tech SC6000 (1,500W ???, 14Hz @ -?dB). DefTech's specs tend to be very "optimistic". IMO, you can get better value for your money.
- SVS SB12-NSD (400W RMS, 23Hz @ -3dB, 2-metre ground plane - should have usable 20Hz or lower in-room extension). A well-rated compact sub.
- Rythmik F12SE (370W RMS, 14Hz @ -2dB). Most of Rythmik's subs seem to extend to 14Hz @ -2dB. Not sure how/why that is. I'm surprised that it's spec'd to dig that much deeper than the SB12-NSD. That said, Rythmik's subs are well-regarded.
I'd pass on all the subs except for the last two, and my choice would be the SB12-NSD.
But if you're tending toward the Rythmik, and since you're looking at ~$1K for the F12SE, you might want to consider the F15 instead (370W RMS, 14Hz @ -2dB). If I'm not mistaken, it will provide greater overall output than the F12SE.