Why don't you dive into the QS8's and find out how they match up? If they don't soudn good together, you can always send 'em back, and all it will cost you is shipping (for around 22 lbs, plus packaging weight).
Consider this: If you can't match the Vienna's with Vienna surrounds or bookshelves (if they even make them), and are unwillin to mix-match you're speakers, then you are going to be relegated to one of the following situations: (1) stereo sound for the life of your Vienna's, or (2) purchase a new, all matching surround system.
In the first scenario, you don't achieve your objective. In addition, what would be the harm of adding even crappy sounding surround speakers to your system. If you're going to listen to all of your music in stereo (pure direct), then justy dont' use the surrounds when you listen to music. But, I woudl venture that even crappy surrounds (barring static inducing paper boxes that rattle and hum, etc.) are better than no surrounds - especially to give you a taste of it all.
In the second scenario, you'll have to purchase the surrounds (along with new front and center speakers) - so the money is already spent.
Therefore, I suggest that you take advantage of the 30 day free trial. If you like what you hear - then, bingo, Bob's your uncle. If you don't, then you have two options - either send them back for a full refund (minus the cost of shipping them back) or you can purchase a new set of matching fronts to go with them (if the back account so allows).
Either way, you've gotr nothing to lose. And considering the diffuse and transparent sound of the QS8s, I'd venture to guess that they will soudn just fine, especially for an exclusively home theater application (music might be another issue).
JUST DO IT....
