Vandersteen model differences/power requirements

The 1 series is a nice speaker, especially for the money and in a smaller room. The difference between the 1b and 1c is not night and day but I would go with the 1c. It is slightly better.
The 2 series is Vandersteen's most popular model and is definitely a better speaker than the 1 series. It goes deeper in the bass and has a little bolder sound. It is a 3-way(actually a 4)It has a 1" tweeter, a 4.5" mid and a 8" woofer along with a 10" active acoustic coupler. The 1 series is a 2-way with a 8" woofer and a 1" tweeter. It is also a transmission line type of bass design where the 2 series is a sealed enclosure. All of this info can be found at the Vandersteen web sight.
The difference between the 2 series lies in the difference in tweeters. The 2 to the 2c to the 2ci and the 2ce represented a successive improvement. The latest 2ce Signature uses the same tweeter as the model 3A. I can say without a doubt it is better than all previous 2 series.
One caveat about the 2ci and the 2ce, the 2ce had a change fron the 3/4" tweeter in the 2ci to a new 1" version in the 2ce. The problem is, some of the earlier 2ce models have the 2ci 3/4" tweeter in them. There was a problem with availability back in the early nineties and Vandersteen used the old tweeter in the early production runs of the 2ce. You do want the 1" tweeter. It is significantly better.
Sound wise, they all have a family signature. The difference is in resolution. I would definitely go with the latest version that I could afford of either speaker.
The 40 watt NAD will be marginal for driving any of the Vandersteen's(if you play at anything other than a moderate volume) I don't think the tube amp will cut it unless you listen at low levels.
My personal opinion(for what it's worth) is to go for the 1c in your room. I think you will be happier with the outcome considering the 2 series take more power to drive.

As I've said many times before, I think the 2 series Vandersteens may be the best value in audio. They do need space, they can be very fussy about rooms and placement. Considering the size of your room the 1's might be the better choice for you.

When I purchased my 2ces about two years ago, I had already purchased a more powerful amp and seperate tubed pre, but just for fun, I hooked the speakers up to soon to be replaced Cambridge A3i (50 wpc). It worked, but the comparison to the 100 wpc amp w/ tubed pre was pretty much night and day. With the Cambridge driving, things didn't sound horrible, just a little thin, and things like soundstage, timbre, and a sense of "air" were very diminished. So the upshot is that you could use the NAD with the 1c's and save up for a more powerful amp down the road. A quick check of the vandersteen website reveals that the 1c's are fairly efficient (moreso than the 2c's) and that the recommended power requirements are 20 to 100 watts.

my first exposure to Vandersteen was as combination of a Vandersteen 1C and a NAD C320BEE, which is rated at 50 watts per channel. I felt that this combination was incredible musical, and the NAD was capable of driving the 1C to very loud levels without too much fuss-- it's an extremely capable amplifier.

As most other people have said, the 1C is better suited for smaller rooms. If that's your case, I'd recommend the NAD/Vandersteen combination in a heartbeat.