Don't do it!
The resistance "looking into" the ac input of each amp will be inversely proportional to the amount of current drawn. If the amps are not pure Class A, that current will fluctuate widely with the music. At times when there is a high volume note in one channel, and low volume in the other, you will wind up with much too high an ac voltage into one channel, and much too low a voltage into the other.
If the amps are pure Class A that fluctuation would not occur, but there still would be problems. If the timing and magnitude of the current surges that occur at turn-on are not absolutely identical for both amps, you could wind up with much too great an ac voltage being momentarily applied to one amp. Likewise, there could be problems at turn-off. And if the amps have a standby mode, during instants of time when one amp is in standby and the other one is up and running, there would be huge inequalities in ac resistance.
Your idea, while certainly imaginative, does not sound to me like a good one.