The way you are configured is pretty good. It could be tweaked to be improved, but not in a major way that impacts your main point about multichannel DSD.
DTC is providing good information, in a general sense, but unfortunately it is not really applicable to your Marantz.
The Marantz does not accept USB input, from a PC or anything else. The USB port is only for the connection of USB storage devices, which allows the Marantz to browse and play the files stored on them, like the audio systems found in cars. The PC cannot play live to it over the USB interface. As I recall it doesn't do DoP either. DLNA is an option, but I don't recommend it, and I don't think the Marantz will do multichannel DSD that way either.
If you demand to play multichannel DSD files without resampling, you may have to invest in a different DAC.
But you should carefully consider DTC's point about audibility. Your Marantz will definitely accept multichannel PCM, so MC could convert and output all your files that way.
You will have to decide for yourself if you can hear a difference, and if that difference is worth spending money on, for a DAC like the Okto DAC8, which is an 8-channel DAC.
Good luck.