Rel Line Array experience


I’m interested in hearing from anyone who has heard a Rel line array (S 510, specifically), or has one in his/her two channel system.  I currently have a stereo pair and am thinking of upgrading by adding 2 more, or if the benefits are worth it, 4.  What will the second or third stack add to my existing Treo CT’s?  Thanks for any help.  
cosmic_charlie
I use an Infinity RS-1B woofer tower (line array). They are very effective as woofer towers and are crossed over higher than a subwoofer would be. It adds image depth and bass power. Not sure what stacked pure subs would do. I'm sure they would work but for the cost I would try to find some Infinity woofer towers or some other high end brand. 
S510s are designed to be used in a line array configuration if desired. Try stacking your two see what it sounds like. I think you will be suprised.