The only way to get outside music sources into a Sonos system is via a Line-In on a Port, Amp, or Era speaker + the Line-In adapter.  However, the Line-In on Sonos are analog, and that device has no line-level analog outputs.   It does appear to have a coax digital output.  You could use a coax-to-RCA adapter to connect the coax out to the Line-In on a Sonos Port, Amp, or Era speaker + the Line-In adapter.

However, I’m not sure what that device gives you that Sonos does not.

It’s an amplifier you need unpowered speakers and doubt it will connect to Sonos at all the DMP a6 could via a line in connection 

Lot of money compared to simply ripping your CD collection and using the Sonos Music Library. 

Once I ripped my collection my CD players weren't used, then moved to the spares closet and finally donated. CDs are under a bed just in case, been there since 2010 or so.