Recommendations for a new subwoofer?

@cooper52: Though Rythmik designer/owner Brian Ding prefers and recommends line-level connections, he offers his subs with a choice of plate amps that provide both high-level (power amp) and line-level (pre-amp) connections. My attitude on that subject is: Why add the distortion inherent in all power amps to the signal you send to your subwoofer amp? So that your sub suffers from the same imperfections as do your loudspeakers (the distortion of the loudspeaker’s power amp introduced into the reproductive chain)? Imo that’s a questionable approach, especially with a tube power amp.

I say, go ahead and get that T/9X. I might even got with a T/7X. I'm a fan of smaller subs for music. You can never go wrong with a REL. They seem much more musical and easy for blend with your speakers than a lot of other subs. Other subs may have more power and can go lower, but that doesn't make them sound better, at least not to me. Whatever you decide, enjoy your purchase and enjoy the opportunity to audition some new stuff. 

@cooper52: 1. "what would be a suitable replacement for that sub?" 2. "despite my previous experience with REL, is that it doesn’t rely on an app to get it dialed in to my system," 3. "Whatever sub I wind up with will have to have speaker-level outputs, because my integrated (ModWright KWI 200) doesn’t have a sub-appropriate input." 4."if I end up with a sub that has speaker level outputs but not a speakon connection, what would you recommend for cables?" 

1. As @deep_333 described, despite their use of the word subwoofer REL only manufactures Sub-Bass Systems (-6dB add on woofers).

From REL’s brochure "REL subwoofers (I still like our original term Sub Bass System for its more complete description of what we do)"

If you or any of the others here recommending sub-bass systems had the opportunity to experience an in home direct comparison between an actual -3dB subwoofer and a sub-bass woofer, the ability for the subwoofer to reveal the subtle recorded extra low frequency would be undeniably apparent. 

2. Since -6dB systems so dramatically roll off low frequencies their stated low frequency is only faintly audible regardless of how many units are used. Consequently they simply do not excite a rooms standing wave bass modes requiring only a gain adjustment at the expense of the recorded low frequency presentation.

3. & 4.Your ModWright KWI 200 is equipped with a pair of RCA Preamp outputs which you would use to connect to a subwoofer input. Blue Jeans or Monoprice Cable offer affordable custom length and type of subwoofer cable.

The recording industry more appropriately uses XLR termination interconnects. Not to be confused with the pro audio public address industries use of Neutrik Speakon termination at both ends between amplification and speakers. Always consult your amplifier manufacture (not REL) regarding REL’s three wire connectivity scheme to their amplifiers.

If you decide on an actual -3dB subwoofer I suggest its imperative to first preform the subwoofer crawl to locate your rooms standing wave bass modes for to proper subwoofer location options where the subwoofer will best integrate with the room, requiring the least amount of EQ adjustments followed by any further speaker integration adjustments. 

Good luck with your search.

@mcraghead Go ahead and get that Rel T9x

At last the side of reason……

But others will say, joining the side of reason….. is not always a good reason.

@m-db 

Great advice there and overall analysis and choices to consider.

Rel recommend the bass crawl you describe. It is in their set up manual. They even suggest an actual CD track (from James Horners “Sneakers” Soundtrack) for a constant repetitive bass drum strike lasting several minutes, to find the best location.

Quite by chance l had it…….. l collect film soundtracks... Simples!

I started with a Rel Quake 20 years ago….added a second. Graduated to a T7 after one Quake failed after 15 years. So impressed with the T7 l bought a T9i. I have now sold on the T7 and bought a second T9i and now run a stereo pair.

l would have no problems recommending this company to friends or family. Rel only make subs…. It’s what they do.