Vandersteens and subwoofers other than the 2Wq?

With the Vandersteen's, I would go with the 2Wq. It is designed to mate perfectly. Why did the REL stick with you more? You really shouldn't "Hear" a sub. It shouldn't increase the loudness, it should only allow for the lowest octaves to be reproduced. Setup will play a bigger part than anything.
The REL is a nice sub and should mate with the Vandersteen's if you want it to. What I would listen for is does the tonal qualities of the REL reflect those of the Vandersteen 2Ce's. Also, the Vandersteen sub is 300 watts vs 100 for the REL and uses 3-8" drivers instead of a single 10". Also, with the Vandersteen Feed Forward Error Correction using a 80 hz crossover, you cannot dynamically restrict it and/or cause distortion.
With all that said, the choice is ultimately yours and YOUR listening preferences. Need to try both and see what works for you using the 2Ce's with each sub.

There has been a lot of discussion on A-gon over the past 18 months or so about the Vandersteen subwoofers (2Wq and V2W). If you have not perused the A-gon archives, I think you should do so -- there is a lot of information that will be informative for you.

A 2WQ does sound quite good with optimal placement. However, the Vandersteen's 6db/octave crossovers do not allow it to disappear into the soundstage as well as the steeper (and lower) crossovers of the Rels and ACI (Titan II LE and Force). This is especially noticeable when the subwoofer cannot be most optimally situated.

As well as allowing the more flexible placement options that my room requires, my ACI Titan II LE also seems to go louder and deeper than the Vandersteen 2WQ, and (IMHO) it is also a fine-looking piece of furniture (it functions as an attractive end table in my living room).

Setup is also quite flexible in that it can be run Rel-style (with the main speakers running full-range and the subwoofer crossed over below that) or quasi-Vandersteen style, using ACI's 12 db/octave highpass filters between the preamplifier and the amplifier that drives the mains.

I've used both methods to seamlessly integrate my Vandersteen 1C's with my Titan II LE. Each method has its advantages in theory and in practice, but recently I'm gravitating toward the highpass filter method, because it usually sounds a bit less congested and clearer in the lows and mids. It also provides me with extra peace of mind when I play the occaisional explosive movie.

Given my strong Vandersteen orientation, I probably would have looked no further than a 2WQ, if I had been able to get it to work okay in my room. I am very glad that I checked out ACI.

I have the REL Stadium III. It is a wonderful sub-woofer. However Sek, Sdcampbell and others have identified something very important. The Vandersteens, in particular, tend to be congested (to my ears) in the mids. The highpass filter relieves the burden placed upon the mains to reproduce low frequencies and tends to clear up their presentation, while passing the burden for VLF to the sub. This enhanced clarity in the mids is, in my opinion, the primary gain of using a sub with these speakers; not low frequency extension of the mains.

Sek, why do you think that a phase correct first order filter would cause the problems you atribute to the 2Wq? I am stumped! And I also don't understand the placement issues you have with the 2Wq. No woofer works well if it can't be "optimally situated". I get the feeling you never listened to one in your system. By the way why would anyone want a woofer to be able to play louder than the Vandersteen? I would invite you to do a bit more research on the 2Wq. Their are as Sdcampbell says lots of good posts out there on this topic.

Judit, the bass congestion you refer to is in my opinion a room/placement issue and not an inherent quality of the speakers. Yes this is a tricky area to get right in most rooms, but with some effort can be worked out. Yes the woofer does make it much easyer to get it right, as the woofer can go where it needs to and the mains can be placed for their best performance. Do you now own or have you owned the 2's? I tend to agree with MOST of the rest of your post.

Matchstickman,(and Sek for that matter) go to the Vandersteen site and read the article listed under the link for indipendant reviews. Open the link for the 2W then find the Audio Perfectionist Journal article. It will expalin very well the benifits of the Vandersteen unit. I will highlight some here. First the 6db per octave phase correct x-over and second the fact that with the Vandersteen you get the true benifit of Bi-amping. Read it. This guy knows what he is talking about!