I followed the wiki for setting it up with the nvidia-drivers and so far so good.
The big downside I'm facing is, that I don't get any sound at all from neither machine. I have them both hooked up to my sony receiver. The Core is connected with spdif coax, while the MD is using spdif optical. In the webadmin I've set them both to Nvidia HDA. I checked on the core with the alsamixer, that the iec958 is not muted and I cranked the volume up.
On the md I got no such thing, alsamixer shows me only 2 channels: one for PCM one for Front. Interesingly I found in the restricted drivers, that there is an Intel HDA activated, while aplay -l says its Nvidia HDA.
In addition to this mythtv still doesn't want to let me watch TV. The setup complains about the storage groups and the playback quits with "There was a problem displaying this video".
So currently all I can do is watch movies without sound...
Does anyone have any pointers for me, how I can solve any of those issues?
thanks in advance
 the mythtv problem seems to be limited to the MD, TV works on the core...but still without any sound