I have had this problem on 2 different systems, and noticed my girlfriends system has the same problem...During dialogue the volume is too low and during action/music it's too loud. We have to watch movies with controller in hand, and adjust the volume from scene to scene.

What is wrong? Both my girlfriend and I have a stereo setup with 2 speakers. Hers is hooked up to the TV, mine to a receiver (Pioneer). I suspect it's trying to output surround sound and can't, but twiddling with the settings have proven fruitless. Anyone have any advice on how to fix it?

It sounds to me like you are setup for dolby surround but without a center speaker this is exactly what I would expect to happen. Check the Pioneer receiver manual for the settings and change it to two channel or phantom mode.

Yeah - "What he said"

If that isn't it, look for a "dynamic compression" item in the DVD player's setup and turn it on. Then only use Dolby tracks, no DTS. DVDs have quite the dynamic range and this is a common complaint even when they the equipment is running normally. My wife would be a good example. Dolby has a built-in system for evening out the voice/effects volume somewhat.