What to do if the MIDI switching only works partially ?
When using several Le Preamps, connected with MIDI cables, and configured in multi-channel mode (which is the default setting), each preamp will listen to the others :
pressing A on the first preamp in the chain (let's call it preamp 1) will defeat the second preamp in the chain (let's call it preamp 2), and vice-versa. You will find more details about the MIDI implementation in the user's manual.
If pressing A on preamp 1 defeats preamp 2, but pressing A on preamp 2 doesn't defeat preamp 1, the origin of the problem is probably in the MIDI cable.
A traditionnal MIDI cable is a 5 conductors DIN cable, with 5 pins DIN connectors. As a matter of fact, the MIDI protocol only uses 3 conductors, so some MIDI cable manufacturer will only connect 3 pins, leaving 2 pins unconnected.
The multi-channel function developed by Two notes for Le Preamp series uses the 2 remaining conductors to send informations both ways into the cable (something that the MIDI protocol can't do). In order to make the multi-channel function work, ask your retailer for a certified 5 pin connected DIN cable.