On Oppo's website at
Comparison Between 970HD and 971H there is a side-byside feature comparison chart.
At
Oppo 971H and
Oppo 970HD they list the specs for each of them.
I guess one would go with the 971 if not concerned about SACD and DVD-A playing on their Oppo and choose 970 if wanting to play them. Still, there seem to be some unanswered question in the comparison chart for both.
Distilling it down. it seems that if you want the better versatility in video and better picture (unless I'm misreading, and please correct me if I am), you would want the 971. If more interested in the DVD-A/SACD go with 970