Joe, It doesnt matter what the input is labeled on your receiver. If you connect that to your HD-tuner, you'll just have to turn the receiver to 'DVD' to listen to the source. Not too confusing, right??
If I had a choice, and I had only one 5.1 receiver input, I would save it for the DVD player. If you have an extra optical, then you're all set, and you have one for each.
Yes, if you also have an optical input, but that bugger to use too. For which component???....It doesnt matter.