Lot's and lots of audiophiles(with 2 channel hi-end systems) do what you're asking about doing for HT purposes. The problem is that when you do the DD/DTS processing in the DVD player, and connect it(DVD player) to your 2 channel preamp through Analog connections, IT NEVER SOUNDS AS DYNAMIC! I've tried this time and time again. And no DVD player's analog outs(and internal DD/DTS processing, coupled either dirrectly to an amp, or through a preamp/amp combo, seems to pull this off well enough FOR TRUELY DYNAMIC DD/DTS PLAYBACK, as was intended by the mixers!
You would have better overall(especially dynamic)movie playback through your 2 channel system BY EVEN SIMPLY ADDING A RECEIVER AS A DIGITAL PRE/PRO FOR ACOUPLE HUNDRED BUCKS!..TRUST ME!(OR TRY FOR YOURSELF, AND YOU'LL KNOW) Even better, you can buy AN OUTBOARD DD/DTS PRE/PRO SUCH AS A MODEST ACURUS ACT 3, CLASSE SSP25, THULE, or similar, and have audiophile grade quality sonics for movies, and not spend a fortune.
Rember this however, if you do value the sonic capability that's avalable from DD/DTS, YOU NEED AN OUTBOARD DD/DTS PROCESSOR!...there's really no way around it for properly doing movies. Infact, I too use a high end 2 channel set-up with sub, but I loop in a digital pre/pro for movie chores. This is really the only way to do it right it seems.