T think you may have your 100 MB / 5 MB figures backwards. Downloading (i.e., receiving data) almost always has the higher speed compared to uploading (your PC sending outbound data). That was done to make people running web site servers pay for a business internet plan instead of the cheaper ones for home users.
For some ISPs, that's gone by the wayside. My ATT fiber plan gives me 1 GB up and down with no data caps. My setup is as @yage describes above which converts the optical signal into ethernet which then goes to my ATT router. I've got Qobuz and it all works great with the hi-rez material without any special equipment.