Hi Bean, I also connect my Fiio to my car audio using 3.5mm cable. (also using Focal speakers and processor)
Since I am plugging and unplugging the Fiio constantly, my own reasoning is that it best to use different connectors to reduce 'wear and tear'
Looking at the picture, the pin is TRRRS, that is there are 4 connectors and a sleeve The initial "TR" should be left+ and left-. The next "RR" should be right+ and right-. The "s" should be the ground. I believe the cable connects only to "left+", "right+" and "ground". "Left-" and "right-" are unconnected.
So now the question is, is it better to use the non-balanced 3.5mm output, or from the 4.4mm balanced output?
I was in the same boat with my Elear and M11 Pro. So I bought a replacement 4.4mm -> Elear from this seller.