The volume knob affects the headphone outputs only(for now), however, the Light Ring will still show the relative volume level of the headphones, even in none are connected and RCA jacks are used. If it turned red, that would indicate the headphone output would be muted.
When a song first starts to play, the Light Ring will indicate the song format and other data briefly, before returning to the volume indicator function. The videos provide good examples of this.
If you mean if a Windows PC is used to flash new firmware to the T2P, can the same T2P then be used on a Mac as a DAC. While I have not tried it(no Mac), it would work fine.
What do you mean by this?