Curious, why you added the Schiit Freya+ in the first place? What were you trying fix?
Vintage gear can sound just as good as new gear, it has to be maintained, and used correctly. Do you know if your Sansui has ever been recaped, or checked out? Might need all the electrolytic caps replaced, some diodes are out of spec along with a few resistors. Might as well swap out some noisy transistors while you are in there. This can/will transform the sound in a good way, more dynamic range, better soundstage, lower noise floor, better separation, end to end better. While still having the warm sound they are known for.
Would not try to EQ in the Wiim, most of the time they just add noise with a side of distortion. It's a cheap device, would just use the standard output untouched. If you "need" an EQ get the Schiit one, add it in the proper place.
Or as others have said, sell the Sansui, get the Schiit matching amp, it will sounds glorious.