Unfortunately this post is closed: https://support.hifiberry.com/hc/en-us/community/posts/360012029397-HifiBerryOS-and-USB-Soundcard
But I still would like to thank Hagen. Worked liked charm. I also dug a little bit deeper regarding alsa. Everything, of course, is configurable. It is a Linux system. So why not follow the Open Source idea and provide the user a fully configurable system. Especially if all HifiBerry OS / Tools sources are available on GitHub.
I also have an external DSP attached via USB to my Raspberry Pi. I seriously cannot understand, why the HiFiBerry Team is totally against using the HiFiBerryOS with another sound card except theirs. It is just money making, is not?
It would be great, if the HiFiBerry Team could make the HiFiBerryOS more customizable. I mean, you guys could say: Customize as long as you wont, but if you use another sound card except ours, we cannot support you totally fine!