Best SQ ROON or HQ Player into DSJnr?

You can use the search function to find the corresponding topic.
What inside the DSjr FPGA is a well designed upsampling process which upsample everything input. In theory, this type of operation is not recommended to do twice.

See what Ted ‘said’ here:

Also worth reading:
https://forum.psaudio.com/t/upsampling-oversampling-smooth-or-stairs-curve-between-values-determiniation/5791

Ted’s really recommended connection is TOSLink - it allows DSjr to work on a fully electrically isolated ground, which has very good benefits for Jitter control.
Due to bandwidth limitation of the TOSLink, you can only get up to 24/192 audio transmissions (up to DSD64). This is basically the same as the built-in bridge specifications. So if your Roon server and DAC are not too far away, try TOSLink first.