re: amplification, i am more than happy w/a pair of original (rackmount faceplate, usa-made) adcom gfa555's driving my subs. i was running 'em bridged, but w/all the recent talk on this site about bridging an amp effectively making the load it sees halve, i recently switched 'em back to stereo, & yust use one channel of each amp for the subs. as my older-model upright-style larger subs are rated @95db/1w/1m, the 325w at 4 ohms put out by one channel of the 555 is plenty. and, sure enuff, the control of the amp over the speek is yust that much better in stereo-mode. as the latest models of vmps subs are ~92-93db/1w/1m into 4 ohms, (not sure exactly), i'm sure your nad amp wood be more than up to the task of driving any vmps subs.
hope this helps, doug *woodn't trade my sub set-up for *any* pair of rels or velodynes* sedon
ps - mebbe i'd spring for a pair of the largest genesis subwoofer towers, if i had the $$$... ;~)