“Looking at Lumin/ Aurender”
There are couple of Lumin D2 or U1 listed on US Audio Mart and here if you’re flexible with your budget. I am afraid, you’re not going to find a Aurender anywhere close to your budget with BNC output. You would need to step up to a used Aurender N10 for BNC connectivity.
The app interface is a critical piece of streaming experience so choose wisely. The Lumin app is pretty decent but Aurender’s conductor app is the best app after Roon. It’s stable, well laid out and uncluttered in direct contrast with Roon.
Good luck!