That's pretty common for laptops. But as long as you checked all the "volume" locations, that's about it as far as I know.
From the speaker icon in the system tray. To control panel audio section, make sure the pan is in the middle, that the speakers are set to stereo speakers, and the main volume slider is all the way. All this can be done from in there. But there is more then one location for volume. Also use the laptop's function keys to up the volume, as this can sometimes be sepparate from Windows control. And lastly the volume of the DVD playing software itself, may also be sepparate.
But as far as I know, there is no such thing as a software amp.
Im using a bundled, freebie version that came with a Sony DVD drive.
It has in the audio settings a place to check for "Noisy Environments (Recommended for Laptop users)"- with this enabled, DVD audio is about 5x louder than any other DVD player I've used.. and I can actually sneak the laptop speakers down to about 80% and the DVD audio is still much, much louder.. and loud enough to hear sitting 4-5 feet from it with a movie. Whereas Media Player and WinDVD, with speakers maxed out and player maxed out, I can barely hear any dialogue sitting right at the laptop.
Handy for traveling and watching movies in hotels.. Can now prop the laptop on a table and pop in a movie and hear it comfortably on the bed.
You could hook some speakers up to your laptop. I've never really tried it cause i dont watch that many dvd's on my computer, but yeah... probably would make it a little bulky to carry around, and it wouldn't be a very good choice for a plane or car, but anywhere else would be fine.