The intention, I believe, is not for 3 amps simultaneously. It is for selecting between 3 amps using the multiplexor for totally seamless switching. Using the multiplexor is faster than changing the amp channel.
This is exactly right.
I like the Channels, I really do.
But I like them a lot better on effects where you can use parallel routing, because if there's a slight dropout during the channel change, the parallel dry signal maintains a constant signal, with only the wet portion being briefly slient. Chorus, Delay, and Reverb all do well with this kind of routing.
I don't like Channels so much on Amp blocks. The reason is that, obviously, there's no parallel dry signal path. So when you change channels, it isn't perfectly seamless. And you can't do crossfading channel-changes, which are the Most Seamless Change Of All: Blending smoothly from the sound of one Amp Channel to another, over 500ms or so.
Now, with 3 Amps, I could have perfectly seamless instantaneous changes between them (or, jump perfectly seamlessly to a blend of two of them). That would be cool.
But, even more excitingly, I could apply 500ms of damping to their relative levels and assign them to scene controllers. That way, a single button press (changing the scene) would cross-fade me from one tone to another.
So, yes, there's a use for 3 Amp Blocks.
And, as much as I love Channels, yes, there are some scenarios which 3 Amp Blocks can handle, which cannot be handled by Channels.
