Now, I'm confused.

I've owned pretty much every Vandersteen speaker from the 1's all the way up to my current Quatro's.   While I agree that changing preamplifiers can definitely affect the soundstage, I don't think that it should be your first move.  As said before, Vandersteeen's are very sensitive to positioning, especially tilt.  It can make a night and day difference.  They also need space to breathe, so set up is very crucial.  It also happens to be free.  I know that the idea of buying a shiny new toy is always appealing, lord knows I've fallen victim too more times than I'd like to admit, but no matter how good your front end is, if the speakers aren't position properly, you'll never get all the potential out of your system.  Look at it this way, its something you're gonna have to do either way.  I'm spoiled because the local Vandy dealer is one of my best friends, so anytime I make any changes he comes over with his laser levels and spends the day making adjustments.  Its tedious but make a HUGE difference.

+1 maceo23

And room treatment...

I can appreciate all the suggestions for room treatments, but isn't that like putting lipstick on a pig?

I mean, room affects sound/stage, but wouldn't a person want to start with the equipment first?

And room treatments, at least good ones, are very expensive. Look at the OPs list of gear, I dont see that the GIK stuff is similar in pricing. I mean, suggesting one GIK would cost more than his preamplifier or other piece of equipment. IOWs, it does not make sense to me. Yes, the room traps/diffusers will help him, but at what price? and then he never figures out which parts of his audio chain hinder the soundstage. 

I have plugged this before; but in case you missed it there is a CD that helped me do wonders with speaker positioning. I am in no way affiliated or involved, except as a surprised and happy user. It's the IsoTek Ultimate system Set-up disc.