Actually, I'm really refering MAINLY to DD/DTS decoded 5.1 material. As for pcm material output from the analog out's of a good dvd player, that's another story entirely!...to a point.
Yes, often using a good dvd player into a 2 channel preamp and such is going to yeild better results for that application. Infact, my old Panasonic DVDA310 has superb 2 channel pcm and 24/96 resolution output from it's analog out's! However, going from my 5.1 channel out's into just about any pre/pro or preamp setup I know of, for processing DVD movies (DD/DTS material), has NEVER YIELDED anything but flat dynamics and lackluster overall 2 dimmensional sound! I have found this to be the case with every dvd player setup! Probably has to do with a number of factors. Basically, my setup's are digital-in from the DVD player for DD/DTS and PCM some times, and analog in for 2 channel pcm, depending.
I say depending because many of my setup's require bass managment and or "EQ'ing" for best sound, which means running full range from analog inputs (without something like an Outlaw ICBM) often leaves me with compromises in bass management and/or (sometimes, depending) equalization!
There's always compromises one way or another.