Roon does not currently downsample DSD128 to DSD64. Signalyst’s HQPlayer does and there are plans for HQPlayer to be integrated within Roon in future (users will probably have to acquire a separate HQPlayer licence)
I do not know if the planned integration will extend to downsampling DSD. It may be that @danny can say something about it.
I’ll shift this thread into Software for more general discussion.