trying to match gain on differnt amps

Hi all, I have just finished the orion speaker project and had bought rotel amps to power them.

Sorry this question is not quite diy related on the amp side. because of what was available I had to get four amps, two the same to power the woofers and two the same for the mid/tweet.

My question is what is the best method to ensure that the gain is the same on these different amplifiers. I have at my disposal a multimeter and could get hold of an oscilloscope if that would have a distinct advantage.

Any help or winks would be appreciated.

can you get a test CD to play test tones into your amps?
Then just measure the voltage at the output.
Are they all power amps? or integrated?
If possible connect one as pre-power and all three others as power only.
If the Rotels are like other good maufacturers then the whole range will have the same gain but there again they are japanese (far east) & I'm sure they will change these specs from month to month.