Are big subwoofers viable for 2 channel music?

BTW my custom is Duke's (Audiokinesis) Swarm not "custom made by me"
I used the term custom because you could customize the amount of subs, amps etc. when purchasing from Audiokinesis
Duke always suggested the benefits of increasing the amount of subs beyond 4 (6,8) although for space and practical issues 4 is a good number, if I would have the space I would have go for 8 hanging 2 on the ceiling for vertical plane coverage as well.

Miller's 1st reply was right on target

Hello smodtactical,

      I agree with bdp24,   that four Rhythmik F12 subs would perform well in a DBA configuration and that four F18 subs would likely perform just as well but with a bit more deep bass power and impact.
     I think it's important for you to understand a few facts about how humans perceive bass:

1.  We can generally not locate bass tones (determine exactly where the sound is coming from) below about 80 Hz and the deepest bass tone we can generally hear is 20 Hz,  Our bodies can feel deeper bass tones below 20 Hz but we generally can't hear them.  Also, there are very few musical instruments that are even capable of producing bass tones below 20 Hz, pipe organs are the only ones I'm aware of.

2.  Because of this, we perceive all bass under about 80 Hz as mono and not stereo.  Recording engineers have known this for decades and have been summing all bass below about 100 Hz, as well as filtering out bass frequencies below about 20 Hz, since the 1950s.  This is also why you can safely disregard any suggestions of positioning subs in your room like main speakers, with a carefully positioned left and right speaker.
     In other words, there's no such thing as stereo deep bass.  Best in-room bass results will be achieved by operating your subs in mono mode and positioning each sequentially for optimum bass performance.  I can explain exactly how to do this, regardless how many subs you ultimately choose to utilize in your room, in a future post.

3.  Virtually all commercially available musical content produced in the last 80 years, has the bass below about 100 Hz summed to mono and bass below 20 Hz filtered out.  So, even if you did place your subs in a left and right stereo physical configuration, there's a complete lack of content with stereo deep bass to play on them. 
     My main point, again, is to disregard any suggestions or notions of positioning or operating your subs for stereo playback.  Just operate them in mono mode and position each for best bass performance.
    Beyond the above, it mainly comes down to cost and convenience.  The Audio Kinesis Swarm 4-sub DBA system costs $3K and will produce high quality bass in your room down to the audible limit of 20 Hz. I've never auditioned any Rhythmik subs but believe they are high quality subs at reasonable prices.  I also think it's likely that utilizing four F12 or F18 subs in a DBA configuration in your room would outperform the Swarm complete system.  
     Of course, the decision is completely up to you.  I just want to make sure your realize that either Rhythmik option option will cost significantly more and will be less convenient to setup since you'll need to set the volume, frequency cutoff and phase controls separately on each sub, rather than once for all four subs on the Swarm.  
     However, I also believe that utilizing two F12 and two F18 subs would perform very nearly as well as four F18s in your room, helping with the cost but not the convenience.

Later,
 Tim

I just want to make sure your realize that either Rhythmik option option will cost significantly more and will be less convenient to setup since you'll need to set the volume, frequency cutoff and phase controls separately on each sub, rather than once for all four subs on the Swarm.

Not owning a Swarm system I may be missing something, but I would think that having the ability to fine tune each individual sub would give one more flexibility and customization in their setup.  When I set up my four subs I took SPL readings for each sub to adjust the output so that they would be equal from my listening position.  I have one sitting just a few feet from my listening position and another on the far side of the room.  It doesn't seem that having them all at the same level would be a good thing.

Rythmik. At least look into them.

I have a medium/ large area and use 2 HP Rythmik 15" subs.  They do anything you ask them to do. High damping acts like a speaker. Start and stop on a dime. I believe it's the servo design. You wouldn't know I have subs until they're called upon. I use them for music and movies. Actually, you still dont know the subs are there, but I dont have speakers that go that low. They are absolutely seamless. 

I did have my audio set up by a pro. Took 5-6 hours for HT setup, but it can definitely be seemless.

I suggest 2 f18s for your room, then if needed, you can always get 2 more. I doubt you'll need more. You do get a 2 sub discount. 

Good luck