Hi Julian,
Hope this would not be too late for you.
TL;DR:
**If you have audiolab mdac, and wanna use Linux based os just stay away from any pc/micro computer with USB3.0. **
If you have audiolab mdac, and wanna use any pc/ micro computer with usb3.0. Go windows10 or MacOS.
I had met the same issue with rpi4 with Linux based player os.
Quote from JohnW:” Generally MDAC has issues with newer USB3.0 ports (USB3.0 host IC’s do not support the lower bandwidth USB1.1 interface very well without experiencing dropped USB frames).”
Mdac will have usb buffer fluctuation issue which causes pop/clicking/distortion sound.
I have rpi3 and rpi3+ using the player os like moode/ volumio/even rasbian without any problem .Because they only got USB2.0.
But the same os on rpi4 have issues, no matter on usb2.0 or 3.0 port or through hub. Because they are on the same controller VL805. I think that must be something in Linux driver implement.