Hi,
You may need to give a bit more info - some more detail on your setup and configuration.
What settings do you have set under the 3910's menu? Especially under the Audio part.
But as a side, (it doesn't adress your problem

)
You may want to look into, seeing as you have a Denon 3910 and a Denon 3805, a special connection available just for Denon product caled 'Denon Link'.
They have just released the final version of this connection (a firmware update for the 3910).
This 'Denon Link' digitally passes all audio formats directly to your pre/pro; CD, DVD-A, SACD, DVD-V (DD and DTS) etc. all over just one cable.
It'll save a huge hassle of the 6 analog cables, and as long as your amp is setup ok, you should have no problems
Anyways, give us a bit more info on you setup, i'll see if i can help a bit more
Cheers
KJ