Your RS250 is capable of playing DSD512 files natively. I am assuming you are playing DSD files or CD rips stored on your NAS. Your NAS can be connected to RS250 via USB or over your Network. Here is what manual says,
- Select the transmission format(Native, DOP, PCM) of Audio Samples to be delivered to the DAC when playing DSD music files.
- In Native mode, Analog Output (RCA out to your preamp or amp) supports up to DSD512 when playing DSD.