I would like a good quality stereo mic to use mounted at my DVX100 instead of its build in stereo mic.

Maybe also a Beyerdynamic EA86 Camera Shoe Shock Mount and a Rycote Softie if they make one for the AT822.

Can anyone say something about this setup or maybe recommend a better solution?

I like the wide sound from a stereomic instead of a mono mic. I will mix the audio from AT822 with the signal from my ME66 when doing voices.

I'd recommend the AT825 with XLR connectors rather than the AT822 with mini connectors if you're going to use the DVX-100 and want to stick at this price level.
You'll definitely need a furry type windscreen, the AT825 is very wind sensitive.
You'll also need to get a shorter 5-pin XLR to 2x 3-pin XLR's cable. Audio Technica makes one for the AT835ST mic or you can get one custom made.
Which reminds me, the AT835ST would actually be a better choice if you really are set on having a stereo mic. However it's a lot more expensive.
Some other people on this board use the RODE NT-4, but it is rather large and heavy for camera mounting.
I think you could also use a RODE NT-5 stereo pair. This would be fairly inexpensive, would give you 2 separate mics to use and you could vary the angle between the mics if needed. It would require a bit of extra hardware for mounting to the camera though.

Rycote has a winjammer to fit over the supplied windscreen of the AT822/AT825 as well as the NT-4

For the 822
www.bhphotovideo.com/bnh/controller/home?O=details_accessories&A=details&Q=&sku=258921&is=REG

for the NT-4
www.bhphotovideo.com/bnh/controller/home?O=details_accessories&A=details&Q=&sku=277952&is=REG