Subwoofer line array for 2 channel


While browsing high end 2 channel systems on line I'm seeing people stacking powered subwoofers in colums of three and four.Rel has some great pictures of this.Does anybody have any comments or advice on this technique? In my number 2 listening room l have a set of Revel Ultima Gems and have 4 subs now.lve decided to add 4 more and have two colums of 4 behind the speakers. Setting the crossovers at different points seems the technique being used.
So far lve had some impressive results.The spousal acceptance factor is not very high with these systems. 
128x128vinnydabully
Less floor space for sure...All kinds of good things about the stack, BUT the DBA guys will want to spread it and closer to the walls, take a couple of them out of phase, la-te-da.. Same stuff different day..

Now go a step further, with 2 MB columns, and low rider subs (4 will do)
A servo sub are one up again I use 4-6 12" OB drivers and 12  M/B 8" column drivers... DBA is great, been around for 30 years, my way is better, no ifs ands or buts..

Good results... "The hole house quit shaking honey", "what do you think"

60 hz and down is servo controlled Rythmik Amps/ GR Research drivers
60hz to 300hz is DSP controlled Behringer 2496, DIY Columns
300hz to 26k is a passive 2 way quasi 2nd order 12 db XO RMx Elixirs

Not a lot of floor space, but can sure cover some ground.. COLUMNS....

Regards
Many top tier large systems have vertically stacked stereo woofer systems. I use the woofer towers from an Infinity RS-1B. I personally think this is close to ideal.  
I use the woofer towers from an Infinity RS-1B. I personally think this is close to ideal. 
 There is no problem with a stack or a tower of subs but, with only 2, they cannot be spatially distributed to deal with room modes.
I guess the question im trying to solve is:
Is a column or stack of modern day class D amplified subwoofers more effective than some of the older huge woofer columns found in mega systems that use older outboard amplification...l can tell you as far as portability there's no contest....