Saturn, that's a no-no, too. You NEVER want to connect two pre-amp outputs (whether it is a receiver pre-out or a CD player) in parallel, either -- if that is what you meant by the use of a Y-adapter.

The output circuit of one amp would act as a very heavy (low-impedance) load for the other amp. If you are unlucky, you will have a fried output stage. A better scenario will be lots of distortions. Not a pretty picture...