Thats correct, with Coax or Optical digital in, the A6 just shows a minimal playing screen displaying sample rate and volume setting. VU meters can be displayed but no Spectrum or DSP options.
Unknown, but this situation has been the case from day 1 for the A6. The spectrum and DSP options have been introduced via firmware after the initial launch, the developers have implemented these new features leaving the digital in options untouched. The hardware routing of the A6 sends the external digital inputs direct to the DAC so the spectrum and DSP add ons are apparently implemented before the digital in feed and applied to the internal digital source only. So I would guess this situation will continue.
