You've changed two key items at the same time. The 800 is probably the best DVD player and the G68 has to be more capable when it comes to processing surround (with MRC and all the other subtelties of setup) than the G91. The G91 is an all-in-one box and whilst it is no doubt a great unit, spreading the various tasks across two great units should make it better.
Upsampling will make a difference with movies also. I found that when I did the same with my 568.2. Details are better, rear dialogue is easier to follow etc. Even Sky+ now I have it at 96/24 into my DSP's is far better in the rear channels.

So, all said, you've made many changes and all for the better. That's why it sounds better. Congratulations [Linked Image from softronix.com]

Rgds

Nick

Rgds,
Nick