I have a pair of 2CE Signatures. I really, really like the Vandersteen products. I drive mine with a McCormack amp that puts out 185 watts per channel. They do like, and benefit from a decent amount of power, and they are not extremely efficient. My first thought is that the Jamo speakers were more efficient and gave you more output from the NAD receiver, whereas the Vandy's are less efficient, and you get less sound output.....most noticibly on the bottom end. I would not give up on the 2CE speakers. One other thought, have you double checked the speaker cables to make sure they are in phase(+ and - wired the same at amp and speaker terminals)? If out of phase that will tremendously impact the output as well.
Good luck
Good luck