I have spoken to Vandersteen on this as well. I asked for his advice about adding a pair of 2Wqs to my 3A sigs or just upgrading to the Quattro. He recommended sigs and the separte subs because you get the same mid and tweeter drivers plus the advantage of four drivers in the 2wqs.
Vandersteen Quatro speaker - link to info
Shortly after the CES, there were several posts here about Vandersteen's new speaker, the Quatro, which is positioned in the model lineup between the Model 5 and the 3A Signature. I don't know if anyone has posted a link to information about this speaker, but I noticed this evening that the Vandersteen web site now has a description of the new model. For those who are interested, here's the link to the Quatro page:
http://www.vandersteen.com/pages/quatro.htm
http://www.vandersteen.com/pages/quatro.htm