Unfortunately I believe that will be the best you can do. I have a similar setup with a Cox supplied SA 8300HDC and a Panasonic TH-50PX6U HDTV connected via a HDMI cable. I had the same issues with a SA 8300HD box.
My work around is to use a fixed 1080i resolution on the SA 8300HDC, ie. press the remote control
Settings button twice, select
Set: Picture Format: Fixed. Exit then press
Settings once and select
Picture Format: 1080i or
720p or whatever resolution you want.
Of course this presumes you have those resolutions available. See the Advanced configuration section in this guide from SA.
http://www.cisco.com/web/consumer/su...s2/4003114.pdf