if you are going to use more than 1 usb card, plug them all in before you start as it messes up the ms4h sound card and zones if you add another after (although im not sure that a Pi will work well with more than 1 card)
make sure you are using one of the recognised usb sound cards
also when you set up internal zones in ms4h dont activate the msg/gateway app until you have installed the loxone music server in your config and uploaded it, else your ms4h zones wont start at all
i would suggest:
1) add the loxone music server in your loxone config and upload/reboot first and set its ip address to that of your ms4h/Pi - it will show as offline of course
2) add all sound cards you are going to use to the ms4h hardware before you start
4) make sure you follow the logitech music server setup at ip:9000 as in the instructions above, missing this will create issues
5) you can create your ms4h internal zones with msg in a single step now
6) drop your loxone music server zones into your rooms and attach inputs/outputs etc and reload your config
thats it, fairly straight forward