What receiver do you have? Most 5.1 or 7.1 receivers have test tones (pink noise) that enable you to balance the volume (calibrate) your speakers using an SPL (Sound Pressure Level) meter such as the one from Radio Shack.

There are discs, like DVE (Digital Video Essentials) and AVIA Guide to Home Theater that provide similar tones, and do a whole lot more for you as well.

AN INTRODUCTION TO TEST & CALIBRATION DVDS aka "Why the hell do I need one of these things?" (To learn about DVE and AVIA, scroll down far enough to read "THE DIFFERENT DISCS AND THEIR ATTRIBUTES")

Essential Accessories: The Radio Shack Sound Pressure Level Meter

A Quick Overview of Home Theater Calibration

Calibrating Your Home Theater System

How To Set Up a Subwoofer (or Subwoofers) for Home Theater

Subwoofer Setup Guide by Bossobass

Common Subwoofer Set-Up Errors by Edward J M

Jack

"People generally quarrel because they cannot argue." - G. K. Chesterton