I have an old Denon 1500 receiver. It has been with me a long time and I am pretty attached to it. I was going to give this receiver to my son and he was wondering if there is a seperate decoder available that is not to expensive to let the pro logic receiver work with Dolby Digital 5.1. Will there be a significant increase in sound from digital from regular pro-logic? We went from the Denon setup to a new 6.1, but we got new speakers, receivers, etc. so their was a vast difference. Would it be worth it, and if so any recommendations on which to get?