Hi @DirkST,
Good reading! Like how you deductively solved your issue.
I too saw that MPD config was still 48kHz (not sure why I ever said that was standard…), in any case, that should be solved now.
Why does the installation from the plugin store not work? Well it’s some commits behind my personal GitHub repo, and somewhere along the road Jessie was no longer supported by the ‘latest’ SnapCast builds. So I had to lock v0.15 for Jessie in the plugin install script, which should be LIVE now, but I’ve been too occupied to follow all my PR’s. Will be working on the plugin this week. 
Also posted some info here: Snapcast config - #5 by Saiyato
Cheers