No, because Optical cables are limited to 2.0 PCM.
No, because of the optical connection to the Logitech Z906 speakers - it can only support max. LPCM 2.0
Optical S/PDIF supports DD/DTS 5.1 (lossy) bitstream and has as long as I can remember. This is unrelated to the LPCM update in the C9 firmware. I'm not sure what the issue with your PC (2060 Super GPU), but it might be better asked in the main C9-E9 thread, or a thread specific to your PC (2060 Super GPU) setup, if there is one. I would think the issue would more likely be on the PC (2060 Super GPU) end of things.That makes me wonder how my xbox -which is connected to the same C9 with an HDMI- can output 5.1 DD/DTS (i can see my speakers turn into decode mode), while my PC cannot.