How about a “Bus” engine which would accept incoming signals from any track that is routed to that bus. The output of the track could be selected e.g. by long pressing the track number, under the move left/right buttons. The default option would be “Master” and if the user creates a bus, it would appear as an additional option. Or the Bus engine could have a grid or list of all 16 channels for the user to select to route to that particular Bus. If a channel is already routed to another Bus it could be made unavailable (just dropping ideas). The bus name could be set automatically as “Bus 1”, then “Bus 2” etc, with the option to rename it.