Ive taken a different approach and it works OK.
Ive got a Broalink RM Pro and using the RM Plugin (IR commands) I can control my DUO 2.
I say BBC1 and the RM Pro types the codes as per remote control (channel 12 so presses 1 + 2 and OK)
There are a few downsides.
1 - Each command (power, mute etc) is a new device in alexa so there will be 100s if you want to add in channels.
2 - Sometimes all commands with more than 1 button press dont work properly (for bbc 1 above I can sometimes get channel 1 or channel 2 or channel 12.)
3 - Each command has to setup manually in RM plugin.

I looked at maybe using HTTP commands in OpenHAB or Home Assistant but this would take ages to setup and also mean that there would be 100s of new devices (Hue Light) in alexa.

Whats needed is an Enigma2 skill for Alexa that knows the commands from the box and the channel names.
Not sure if thats easily done though.