TX3 mini should have working 2.0 audio out-of-box - no need for a USB soundcard unless you're chasing multi-channel support. We have a sponsor for that work now, but due to existing commitments with the sponsor and the implementor it will be a while before it happens.
G12A/B hardware now has working 2.0 audio and multi-channel should follow (before we see it on GX). I'm refining the config but it should appear in balbes150 images 'soon' ..
Remotes should work fine as long as you have a keymap configured. Infrared Remotes [LibreELEC.wiki] has all the info needed.
Thanks im testing on an m8s pro w and have no sound out of the box (but usb works fine) will do some more trials on remote once i get home.. Also i cannot see internal storage of box so i must run from sdcard.
If you need any help with testing let me know.