Krell Man,
It depends on a transformer's secondary winding's current output for each channel (if sharing a primary winding vs. independent transformers for each channel). A single transformer with 3+ channels will be physically larger to contain the additional secondary windings, but should equal the output current rating of the other secondary windings. Each channel should have its own DC rectification and large filter capacitors as well.
Most multi-channel amps, since primarily intended for Home Theater applications, will contain smaller power supply designs vs. running multiple High-end stereo amps, or individual mono-blocks. The later two options would be my choice if deploying multiple high-end speakers with low impedences played at demanding listening levels (HT or multi-channel music). Most people can't tolerate watching movies at sustained levels unless an action flic, hence the typical 100-150 watt/channel amps.
Now, some cheaper amps, integrateds, or multi-channel amps will often share a single large power supply, but with increased cross-talk and other audible compromises when driven harder.
Just a thought.
