I ran into a problem enabling zone 2 on my RXV2500. It ended up being operator error in my case. I was able to turn on zone 2, but wasn't getting any sound. Come to find out, when I powered up zone 2, I wasn't hitting "zone 2/CD" (or any other source for that matter). You'll know you hav it right when the LCD shows ZONE2/CD. At that point, you should be able to control the volume for zone 2 independent from the main source. This may or may not be happening to you, but I thought I'd pass along.
Good luck. Kevin