MIDI handling issues with the Line6 HX Effects
If the programming and channel switching of the AMP1 Mercury or Iridium Edition does not work when using a MIDI controller, the most likely reason is that an ambiguous MIDI command - or even several MIDI commands - are being sent one after the other.
Important info: AMP1 Mercury Edition and AMP1 Iridium Edition only understand unique MIDI commands. If an ambiguous command, or even several MIDI commands, are sent one after the other, the amp cannot process it, and therefore does not react.
HX Effects: Turn off MIDI clock and MIDI PC TX
By default, the HX Effects sends two MIDI lines: before the actual MIDI command, the sender address of the preset is sent. This must be turned off in the HX Effects, otherwise the AMP1 Mercury/Iridium Edition will not be able to process the commands: Turn off MIDI clock in the Global Settings as well as MIDI PC TX on the 3rd screen of the MIDI settings!
Patrick's quick step guide
For a quick step guide on how to make sure the AMP1 and the Line6 HX Effects work with MIDI, check out this article!
By the way: The AMP1 Silver Edition is equipped with different software. This software does not recognize the additional MIDI information sent by the HX Effects, which is why the amp reacts as it should when programmed and controlled by the HX Effects.
In other words, the problem does not exist in AMP1 Silver Edition. So, if an HX Effects can program and control the AMP1 Silver Edition correctly, but not the AMP1 Mercury Edition or the AMP1 Iridium Edition, it is almost certainly a case of the "bug" mentioned above.