maybe you should contact the khadas team and offer them in on the deal, and use them as an agent ?
it's a niche market, and other than trying fleabay, you will be struggling to reach the appropriate consumers
however, khadas may play, because their cases are aimed at micro home theatre setups that *might* add the tone board, whereas the audiophile market are either sceptical about "cheap" excellence, or snobby about their estabished name brands, so your buyers will be a subset of khadas aware bleeding edge audiophiles - and personally i don't find the khadas case attractive - but yours certainly is
just my 2c worth
plan b would be to put it up for sale here :
https://www.audiosciencereview.com/forum/index.php?forums/audio-equipment-for-sale.29/
and of course, here :
https://forum.khadas.com/c/hardware-and-peripherals
any of the audiophile forums might get some interest also
good luck; i'm watching with interest...