BTW I just tried AGAIN to get windows network sharing going and this time it actually worked! All I did different from last time is reboot the PC and now it actually worked! So in 'files' I went to the 3 dots to add the server, then just put in the IP of my windows server (192.168.xxx.xxx, so I used the IP instead of computer name, also no "SMB://" in front or whatever, really just only the IP) and then it asked for username/password. As username I just took my admin username (if you open C:\windows\users you will then see a directory with that username) and my windows password and it worked! But again, as Serviio works really well for me already I guess it doesnt add much, though the nice thing is that I can now also use other players that dont work with DLNA.
Of course you need to have configured your windows share and setup your windows correctly, which is a pain in itself but oh well, had that done a long time ago.
So this is a workaround until they can get the SLR player working of course at full quality