How to perform a gain match two amp for bi-amping?

How to perform a gain match two amp for bi amping(passive) if they are the same made but different model has different power output(2 MacIntosh)? However both of them have output control L/R too.
Just check, their web site have the 10 free tips section which describe how to calibrate a bi-amping system.
It's easy to match gains of the two amplifiers. Just feed them both the same signal and put your voltmeter between the two high signal (red) terminals. Adjust gain so that the meter reads zero.

However this is a complete waste of time because your HI and LO speaker drivers probably have different efficiency. So what you need to do is get a sound pressure level meter and adjust the gains of the amplifiers so that each one, when playing the same signal, produces the same loudness.

And when you are all finished with this, adjust the gain so that the music sounds good to you.
put a white noise source in your cd player. Play the white noise and adjust the two sources until there appears no seams between the hi and low.

Once that is done, you can adjust the volume to your most likely listening level.

Some testing cds would have white noise tracks.
seems to me music works best when I ajust mine,when I use test tones I allways get to much bass