Standard Midi channel has two additional features in Expresseur.

The first one is about Track, to group notes according to their musical role (and not according to their Midi sound)

The second feature is about channel extension.
Expresseur cannot avoid two notes of same pitch on the same channel at the same time.
To solve this issue, you can ask for Midi channel extension : when a second note of same pitch must be played on the same channel, the note is routed to an extended channel.
Expresseur can calculate automatically Midi channel extensions, according to the use of Midi channels in the Score and Translator (if the option is checked in the Hardware tab, section tuning).
Extensions are only possible if the 16 Midi channels are not used in the Score and Translator.

Extensions of Midi channels are displayed on the Monitor. Midi channels wich are "grouped" in the same extension are linked with a small grey line.