i heard a $1200 rel in my home; i've heard the 18" velodyne in a store. bottom line: i wouldn't trade my pair of vmps larger subs, adcom gfa555 amps, & marchand deluxe xm-9 x-over for a *pair* of the top-line models from rel or velodyne. i might consider a pair of the servo towers from the old infinity irs models, or the sub towers from the $130k new genesis model. or, a pair of bag-end's largest double 18" subs, w/their $3k elf processor. but, since my system as described cost only $2400, & that was buying the fully-tweeked subs & x-over brand-new, i'd have to win the lottery first... ;~) used, i'd look at the entecs mentioned above, or the five driver per side kinergetics research sw800's... go to vmps' website & check out the specs on their subs - nothing can surpass 'em at *anywhere* near the price. only a few can even *match* 'em. and, their sound matches their specs.
doug s., no vmps affiliation, just a satisfied customer