You can, of course, open the instrument that the MIDI channel is directed to with the little keyboard icon to the right of the MIDI channel selector in the Inspector.
But to open the channel editor for the Instrument/Instrument Track you can use the “e” button on the right side of the Channel/Instrument Tab in the Inspector for the MIDI channel (about half way down). Not sure about a key command.
Only thing is this will change the selection to the Instrument Channel or the Rack Instrument.
But I’m not sure that you can have a Channel edit window open anyway without the corresponding channel being selected, so . . .
I don’t really use the midi channel editor either.
As far as I know there isn’t a keyboard shortcut for this. All channel editors are connected to the “e” key so changing one would change all.
However, if you open your midi channel editor with “e”, to the right of the channel name at the top, next to the magnifying glass icon is a right arrow. That takes you directly to the instrument channel.
So its two steps instead of one, but still beats scrolling.