So I started a fresh project. One song and one part. Created a stack, and selected channel 15 from my MH interfaces. Then decided I wanted to have a basic guitar set up in a track, so I created a track. Switched the Stack input to Track 1. Tried to change the input on the track to ch 15 - it is no longer a visible choice. Even after saving and quitting VST live. Started a fresh project but 15 is still not visible. Ah OK - I see what VSTL does, it now adds this as an input nit knows about and puts it at the top of the list, curious!
In all your mails you appear to omit the Devices/Connections dialog. You should have a look there.
When you select an input or output anywhere in VST Live, you are presented connections (ports) that have been created by using the plus (“+”) button in Devices/Connections (or by assigning from menu, see below). This has a name that you can change to your liking (left side), and an associated hardware (or virtual) port (right side).
In addition, the menus offer the “raw” hardware and virtual ports. When you select one, you are given the option to name it; if you don’t, the user defined name is set to the harware port name. Then a Connection Port is created for you. Note that the port names (right side) are provided by the hardware driver, we cannot change those.
The additional option to choose a hardware port directly - when no Connection is yet assigned to it - is a convenience function. It’s best to first create connections, name those for good structuring, and use those.