Gain matching of power amps

I see no point in matching a gain. How can you controll it? Even if you find matched gain amps most-likely they will have different sencitivity. The input sensitivity of amps of different brands is different by non-negatable values by tenth fractions of volts or even by whole volts.
On the other hand you can use SET amp to drive your tweeter/midrange and 200W SS amp to drive a woofer if you have an active filter or crossover.
If you don't have an active crossover you might consider using two of the same brand matched amps for tweeter and woofer.

Matching the gain is very important. It's true you can't control it unless the amp has a volume control. It is function of the amplifier design. But different gains will result in different powers being delivered to different drivers with the same input. Not good.

Woofers require more power than tweeters so you can use a lower power amp on the tweeters as long as the gains match. Most people would recommend using identical amps or at least from the same family. Say a Levinson 331 on the tweeter and a 333 on the woofer.

You can skip the rest unless you want the math behind it.

Gain is the ratio of input to output voltages. An amp with 29 dB of gain amplifies the voltage 28 times ( 1 volt in results in 28 volts out). An amp with 40 dB of gain amplifies the voltage 100 times. Assuming an 8 ohm load, the 29 dB amp with a .25 volt input would deliver about 6 watts. The 40 dB amp with the same input would deliver about 80 watts. This is assuming the amp is capable of producing that much power. If not, it will clip.

Using these two amps to biamp would result in 13 times more power being delivered to the speaker hooked up to the 40 dB amp. Clearly, an undesireable situation.

Sensitivity is how much voltage it takes to drive the amp to maximum output. It is really just another way of looking at the gain. It can be calculated if you know the voltage gain and the maximum power rating of the amp. If the two amps have equal power ratings, the amp with higher gain will clip first and is said to be more sensitive. So it really doesn't matter unless you drive the amp into clipping.

voltage gain = output voltage / input voltage
dB voltage gain = 20 log voltage gain
power = voltage squared / resistance

To get from dB gain to voltage gain, divide the dB by 20 then take the inverse log of the result (raise 10 to that power).

29 dB / 20 = 1.45
10 raised to the power 1.45 = 28.2
40 dB / 20 = 2
10 raised to the power 2 = 100

Sorry, that may be more than you were asking but I have too much time on my hands and I wanted to given a reason why the gain was critical.

Your closer bet between the McCormack and Classe is the Classe amps which all have an output gain of 29.02db

I agree with Herman. Having worked with many multi-amp set-ups, you have to do the best that you can possibly do to gain match the amps. If you don't, you'll run into some very "strange" problems in tonal balance and dynamic range that could vary frequency range to frequency range. Sean
>

I've said it before, that Sean seems like a very reasonable and wise person.