It is my impression that Richard was slow in coming out with a 5/5A because he did not see an easy, cost-effective way to improve upon the 3A (he does not beleive you can just create a bigger box, add more drivers (bad in prinicple), charge more, and say it is improvment).
The 5 series (with essentially the same tweeter and midrange as the 3ASig)took a more sophisitcated approach. Internal Powere susbwoofer, and low bass equalization). This techncial improvment (rather than more drivers, bigger box)helps produce deeper bass and permits ideal placment for soundstaging, while contouring bass about to fit your room.
It seems to me, that as such, the Quattro is more than just a glorified 3ASig, but a significant step in providing the susbwoofer and bass shaping capabilites of the 5s in a smaller package. This, of course, does not mean that it will sound better than a 3A/2Wq combination - but it should add some of the powered subswoofer enhancement to the 3As on their own, but without having to add two large boxes to your lisenting environment - this is a good thing if that envirnment is also your living room and you don't live alone.
I'm looking forward to hearing the Quattros.