To me, buying a Dolby Digital decoder in a DVD player is a waste of money. Between the two, DVD player and A/V receiver, the player is MUCH more likely to be obsolete in a year or so. Receivers can last upwards of 4 years if the accounts from Audio Review are any indication. Given how quickly DVD technology is advancing (progressive scan, ColorStream output, Nuon, etc.), you'll likely want to replace the player in a year or two.
Invest in a high quality receiver with a decoder and buy the least expensive DVD player with the correct audio and video outputs that your receiver and TV can handle. That way, when the newest DVD technology comes out, the DVD player can be replaced with the same criteria, and you don't have to waste money buying another decoder.
That's what I did at any rate. It made sense to me.
