What is wrong with a sub?

@mkgus, thanks for that.  My one REL i7 I rarely hear.  Sometimes I do mess with the volume on it and pump it up beyond the music levels, but normally just because I want to wake everyone up.  

Got me thinking if 2 and 4 are better, is there any reason they should all be the same?  Could you mix an i7 with i9 or other brand?  I would tend to shy away from mixing brands.  But when I think of "real" bands and or orchestra there are different low end sounds of different power coming from different locations.  Maybe they balance those, just the base drums are not always center.  

I don't know what DSP is relative to subs.  I assume this? 

I mix 2 RELs from the same UK made era, a down-firing 100 watt Q108MKII, and a front firing Q150e...the synergy and tonal similarity between these two is remarkable, and they sound great.

Subs fill in the 'bottom' that the majority of speakers can't 'reach', w/out distorting their 'upper' frequencies.  Case in point:
 
I happened to be @ a instrument b&m store where some musicians started goofing about with various 'toys'.  While the 'regular frequencies' (80hz+) were covered by the monitors Just Fine, the 'subs' (which had 'ribbons' @ their ports, wagging about...) were 'filling in' the bassline that the monitors 'faded' from.  So, I took that as an 'instructive moment' that Any speaker shouldn't be expected to cover Everything....esp. when it came to moving 'bass line air'....since bass is mostly 'air movement' @ a major (and physical) process.  The aforementioned 'ribbons' were wagging about, in and out of their ports.  It's just how much 'air' you can excite, pure physics....

You want 'concert sound'?  Subs.

I'm too new and inexperienced to take a side.  But as I posted - I like tube amps.  I like how they sound.  As such at reasonable price range tube amps there are no ribbon speakers I can use.  The subs having their own amps move the air fine.  I also like the argument that the position of the subs may not be where the mids are.