The amp is not the problem--I drove my 2CE Sig IIs with the NAD C372 and had bass as deep, tight, and tuneful as I could have asked for. It has plenty of power and current delivery. To repeat what some others have said, triple check to make sure you have both woofers wired in phase--if the polarity on one is swapped, each speaker will cancel out the bass produced by the other speaker. Swap the + and - on one speaker and see if the bass improves.
After that, try working with speaker placement based on the very good Vandersteen instructions (measuring your room and dividing by odd integers). If you don't have the manual, they're available through Vandersteen's website. Taking the time to do this can make the difference between fantastic, full sound and MIA bass.
After that, try working with speaker placement based on the very good Vandersteen instructions (measuring your room and dividing by odd integers). If you don't have the manual, they're available through Vandersteen's website. Taking the time to do this can make the difference between fantastic, full sound and MIA bass.