scofow - its pretty easy. Just turn up the volume a bit - set your SPL meter so its registering well - I like to set the DB setting so that its reading around 0db on the meter - for me thats like 70DB. I use the radio shack meter. Use C weighting so its a bit slower and easier to read.
Then just go through the surround setup and adjust the volume on each channel until they are the same, or as close as you can get to the same.

Before you do all this, run the auto setup so it will identify the distance measurements for you - for me this setting is accurate - however others have had to get out a tape measure.

This is what I do, hopefully I've been doing it correctly! I'm sure someone will chime in if I'm wrong. Good luck.