Re: "Airpod Max audio input gen 1 : I understand that the gen 1 airpods max can accept a audio line in signal with a lightening to stereo mini plug adapter. I can't get this to work! Didn't work on my recent flight, and I can't get it to work with any other devices."
Am no expert in this field, yet your post surely deserves a response.
Seems Apple's cable brings audio to the AirPods Max,
whereas most generic cables take audio in the other direction eg: to a speaker
Wondering whether Apple support's articles (links below) can help troubleshoot your difficulty
Connect and use your AirPods Max - Apple Support
Apart from wireless connection with devices like iPhone etc:
Eg: Above article says:
"Use AirPods Max for audio with a 3.5mm audio source
You can use your AirPods Max in wired mode to connect to analogue sources:
- To use your AirPods Max in wired mode, plug a Lightning to 3.5mm Audio Cable into your AirPods Max (Lightning) or plug a USB-C to 3.5mm Audio Cable into your AirPods Max (USB-C).
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More info: Set up AirPods Max with your Mac and other Bluetooth devices - Apple Support
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Resource: AirPods User Guide – Apple Support : AirPods User Guide - Apple Support
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AirPods Support Website: Find all the topics, resources, and contact options you need for your AirPods....
AirPods Support - Official Apple Support