More alternative sources per channel

Right now we have “Main” and Alt” per input channel to preselct sources. I’d like to expand that to four, like “Main” and then “Alt A” to “Alt C”. A nice addition would be the possibility to rename them globally, like Alt C becomming “VirtSC” for Virtual Soundcheck or similar.

The absolute icing on the cake would be the possibility to optionally premix those sources before channel processing.