imho, my humble pair of bridged adcom gfa-555's are better than the amplification in *any* powered subs. also, my marchand deluxe xm-9 crossover is better than the x-over in *any* active sub - more transparent *and* more flexible. combine these with subwoofers that don't try to alter the laws of physics (i like my vmps larger subs), and yule end up w/bass as good as yure gonna get, w/o blowing the budget. *real*, deep, textured, tight, accurate, un-distorted, hi-level (if/when ya want it), BASS...
i tried a retail $1500 rel (stratus? storm? - don't recall...), and for music, frankly, it was a joke, imo - one-note thump, & not wery deep, at that. mebbe two wooda worked better, but, then it wooda cost more than my present set-up, which except for one of the amps, was purchased brand-gnu...