I have the same setup and i prefer below, but it needs manual switching in C298 to select RCA/XLR and A6 volume passthrough switching.
My setup is NADC298 used for front 2 channel amplification from cinema50 external preout.
Mostly for music, i use direct (no room correction softwares) , so from Eversolo XLR out to C298 XLR IN . In this case you need to switch the 2 dip switches in back of C298 to XLR input. This is really great for direct music listening and my favourite for music.
To hear music through DIRAC+subwoofers (from cinema50) , i have also connected the Eversolo RCA out to cinema50 RCA IN.
While watching movies or sometimes music with some coloring and subwoofer, i use RCA from cinema50 to C298, here you have to select the 2 dipswitch to RCA.
There are 2 caveat's here. First is manually switching the dip switches in C298 to select XLR/RCA and second is you need to switch back & forth the volume passthrough in A6 when you are playing through marantz , but for me it works , but wont work for many
.
Caution - remember to set the volume limit start up to -40 in A6 to accidentally protect your speakers, if you forgot to switch the volume passthrough off while playing directly from A6 to C298. With proper saftey settings in A6(start up volume limit function) , it is safer even if you forgot to switch the volume passthrough in A6 and i tested it as well.
This procedure is bit complicated, but its safer and you can use DAC from A6 to both cinema50 & C298.
This works for me as i only see movies in weekend , so 80% of time music .
You could also use HDMI out from A6 to cinema50, but then A6 DAC is better compared to Cinema50.