At Lexity we bounced everybody who wasn't using IE8 or better to a page that showed them how to upgrade, and specifically encouraged Chrome Frame for those who were stuck with IE6 or IE7. This was very simple to do; all it took was a few conditional comments: http://blog.lexity.com/blog/2011/12/27/browser-not-supported...
I can understand why you make the requirements for your app very clear. I cannot understand why you'd chose to bounce potential customers from your website based on their browser. Isn't this just you failing to provide information to people who have made an effort to contact you and ask for it? I ask this next question gently: Have you checked you're not bouncing people using assistive technology?
Sorry to sound short about this, but it's the same sort of thing that happens when a road turns into a freeway. For everyone's safety, you don't get to ride your bicycle.