The input impedance is what is presented to your source - streamer, CD player etc.
50K should work with any source device, but some may not work so well with the 10K loading.
The amps will be fine with either one.
And we can hope that they will!
As I have one that is what has been delivered thus far, maybe a little time with my soldering station and perhaps a dab of silicone...
I have not opened mine up (yet), but this begs the question: how hard might it be to relocate the IR receiver?
My simple solution so far is to turn the Topping stack about 25 degrees counterclockwise as viewed from above in my audio rack. :cool: