You'll be rewarded if you can, Shoe...
A VR920 center would match up perfectly with the 940s both sonically and visually, however they can be a bit difficult to find. I've had both the VR920 and the VR12 and while both are very good centers, the VR12 is the superior center.
Calibration can make a world of difference in getting the proper levels for your setup. Quite often, you'll have overbearing mains, too lively surrounds or a recessed sounding center, which leads me to my next response on one of your questions.
As for your question regarding the BAs and Def center not being in harmony, this is commonly referred to as 'timbre' matching. This is generally why you want to go with the same speaker line or manufacturer for, at the minimum, your front sound stage (e.g. L/C/R) and possibly all five or seven speakers in your setup. The front sound stage carries between 70-80% of the soundtrack for movies and as such, panning effects from left to right and back need to be as seamless as possible. Using the same model line of speakers will almost assuredly guarantee you of this. Fortunately, most speaker manufacturers tend to have very similar timbre for their different model lines, within reason (e.g., speaker size, low end Vs high end models, etc.), so you can typically use a relatively similar center speaker from the same brand to match up w/your mains and other speakers in your system.
As for your upgrade question, I think you may be right that the VR2s might be a little too much for a room that size as the '10' is a little narrow for towers of that size. The 920s should provide a good sound stage for that size a room, so w/out going to VR2s or VR3s, I don't think you'd be getting a substantial upgrade.
Just out of curiosity, what kind of sub are you using? A solid subwoofer properly calibrated w/the rest of your system can make speakers that may have seemed a bit lacking suddenly come to life. I would suggest the center upgrade/change first, but this may be a consideration as well... -TD
