yeah I've got a really nice Yamaha Prologic receiver hooked up to a Toshiba DVD player with built in DD. For comparison, my roommate has a Yamaha receiver with built in DD hooked up to a Sony DVD player. Basically, his system blows mine out of the water. But I don't really want to plunk down 500 bucks for a new receiver
A good Dolby Digital/DTS decoder is the Technics ACH500D. Do a search on egay and you'll probably find one.
Of course with this kinda thing, you gotta trust your own ears. Go to a Soundtrack or something and listen to onboard DD vs outboard DD. Listen for yourself to see if you can see a difference.
IMHO, for the money its worth getting DD on the receiver.