Here ya go.....
http://www.timewarnercable.com/northeast/support/navigator/faqs.html
I'd give you explicit directions, but one of my son's friends is playing video games right now. When you select your resolution(s) pick 1080 and 720....and for the picture size you want to select Stretch.
P.S. If your picture is grainy you may have a signal issue and if I were you I'd schedule a trouble call. There's no charge for that.
P.P.S. I'm assuming the Buffalo Division has the new Navigator.
P.P.P.S. I have the 8300HDC DVR and I have no issues with it.
Hope this helps.