It is possible one of your rims are warped. It does happen and you'll be banging your head against the wall trying get it ballanced/vibration-free without success. I'd try the Hunter Road Force Balancer and if you still have the problem I'd be on the phone to Tirerack. You know the vibration is not caused by a defect in your car because you are vibration free with your regular set-up. So, it has to be an issue with either one of your winter tires or one of the rims. Lots of luck. (I have an appointment to get my winter setup installed on Monday. Ugh! Did I mention I hate winter?)
2011 535i xDrive, Dark Graphite Metallic, Veneto Beige Dakota Leather, M Sport Package, 316, 322, 3AG, 5AD, 5AG, 5DL, 609, 620, 655, 677, 6FL delivered Christmas Eve '10, Mods - quad tips, 20% tint, JB4.