This is how I do it with my Yamaha receiver:
The test tone first goes to the left speaker, I have the trim for that speaker set to 0db, I then raise or lower the MAIN volume so that my front left speaker is reading 75db. This speaker is now my reference speaker for the rest of the speakers.
I then goto each other speaker in my system, KEEP THE MAIN VOLUME THE SAME, but change the individual "trim" db for each individual speaker so that it reads at 75db.
There you have it!
Its difference for all receiver companies, but thats how it is done on my Yamaha. I hope this helps!
