Why not deal with both?
After experiencing the low frequency response musical deficiency with a REL I'd forgo the two -6dB@30Hz 10" T7x, 0-180 phase switched sub-bass woofers @ $2600. I'd choose something like two 12" -3dB@18Hz Rythmik L-12 subwoofers with variable phase and direct servo @ $1582 (or $2254 loaded) and put the $1,000. difference towards a new cartridge.

