Are REL the most Musical Subs?

And like REL subs, many of the Rythmik plate amps provide the ability to be connected to either a low-level source (a pre-amp) or a high-level one (a power amp).

If I can add something here, all my friends with six figure and multi six figure systems are running the JL Audio Fathom or Gotham subs.  Either in pairs or 2x pairs.  The reliability issues with the top of the line JL subs has been debunked, they are made in FL USA, I don't know of anyone who has had issues with their top subs (maybe the budget end of their line).  REL subs are made in China. The JL subs have more user control, i.e. they have a fully adjustable phase control where REL just has a 180 degree shift available which is a deal breaker.  The JL subs also have an extreme low filter which allows the the very lowest frequencies to be boosted or rolled off as the room demands.  Also, they come with a calibration mic to allow the built in DSP to make room corrections for nodes and modes while the REL does not.  The JL subs by far have the most punch for the footprint, so if space is an issue they will absolutely eat the lunch of any similar sized sub.  I have 2 JL Fathoms in my main listening room and have had no operational issues with them.  I have two SVS subs in my HT room and both of them have had to be serviced.  Good hunting and cheers.

I think that if the post had read "what is your preferred subwoofer for music?" a good number of people would have said REL.  I've watched a number of review videos and many people feel that REL is the best choice for them.  Lots of very positive reviews. I can't say that they are the best, but I can say that they perform extremely well for me and a ton of other audiophiles. 

The dichotomy pointed to with regard to music vs. home theater oriented/labeled subs isn't one to follow with necessity, but rather one that rests with either camp and their potentially self-inflicted limitations. Some if not many of the so-called music oriented subs simply lack the capacity first and foremost to properly handle the demanding low frequency material found in a range of movies on Blu-ray/4K UHD's, while also being restricted into the infrasonic territory. Conversely some Home Theater co-labeled subs may be hellbent on squeezing that last ounce of extension out of a small size factor (albeit typically with larger driver diameter), with all that entails and which may lead them to integrate more poorly with main speakers.

It seems to me though that when overall sub size and driver diameter exceeds that of the more "hifi"-oriented or -accepted sub variants/brands they're automatically relegated into the Home Theater segment (and the associations that follow), which is really a load of B.S. Look at REL: they're small and there seems to be a consensus about their integrating very well with main speakers, hence their popularity in audiophilia. Take then, say, JTR and one of their single or dual 18"-loaded subs of more prodigious size, and mostly there wouldn't be a bloody f*ck of an audiophile who'd give them any serious notice because they're (much) larger, not least the ported variants, and oftentimes more functional looking as well, so naturally they're just about blowing off the roof of one's house, right? Wrong. 

What many still don't seem to understand is that with subs you can "have your cake and eat it too," it's just a matter of proper capacity and sufficient* extension from a design that lets size have its say. A well designed and constructed, large and efficient sub will, as always with some groundwork, be able to integrate smoothly with main speakers and accommodate music and movies alike - in both cases even more so than some puny cube of an inefficient sub (unless with a multitude of them). It's not about either/or (i.e.: music or movies), but doing it right from the outset and thereby covering both bases at once. 

* A word on "sufficient" extension. This is an area of debate, but first of all infrasonics do make a difference with movies, although for proper effect and those very low frequencies to be truly felt you need prodigious displacement and a lot of power. Some also swear by infrasonic capabilities with music reproduction and its deemed importance here, but subs tuned that low to my ears don't always sound as "alive" in the midbass region. I've found that covering down to an honest 20-25Hz area is plenty deep for most occasions, even with movies, without negative impact on the midbass area, and this way one can also maintain high efficiency without ludicrously sized sub enclosures (i.e.: 20-25 cf. per cab). 

All REL are -6dB@ their lowest frequency and were termed  "SUB-BASS SYSTEMS" by the initialed developer manufacturer Richard Edmund Lord on his Operating Instructions.

Regardless of what their product is called today simply matching the REL volume level to your main speakers is not subwoofer low frequency integration. Their dramatic -6dB roll off at their claimed low frequency prevents them from exciting standing wave modes and allows them to be located most anywhere in the room. This locating convenience comes at the cost of discreetly amplifying and adjusting that delicate sub sonic frequency foundation by a few dB that so many recordings poses and you're missing. 

Like most things in this hobby, if you've never heard the potential there's a good chance you'll be satisfied by using a sub-bass speaker simply doubling your main speakers limited low frequency.

"schlepping the sub over the basement testing placement spots,but with advances in DSP I’m now hoping to place the sub next to the rack"

I'm going to assum your potent Paradigm subwoofer was improperly positioned and adjusted resulting in never experiencing the potential of this -3dB subwoofer. Had it been, you would have returned the REL the first day.

With the sub temporarily located at the listening position a low bass cadence is played through both the speakers and the subwoofer. You simply walk around the room making note of the standing wave modes (usually along the side walls) where the low frequency cadence tones sound their best.

DSP is not a panacea to ameliorate the improper but convenient subwoofer location.

Its an amazing thing to watch while the low frequency cadence is being played through the speakers and the listening positioned subwoofer to see the BINGO! on the face of a novice when they hear the standing waves bass mode in THEIR room for the first time.

THIS is the first step towards subwoofer musicality. Sub-Bass Speakers need not apply. They just don't go low...so, no.