At least on my NAC 332, the top-most RCA input (of three) is physically labelled on the back as Input 3, and the default assignment of that input to the front panel buttons is listed in the User Guide as the ‘Tuner’ (section 3.2 on page 4).
However when I connect RCA cables to this input from my streamer (and set streamer output in settings to RCA), it turns out that I have to select the ‘Preamp Streamer Input’ in Settings / System Settings / System Automation to ‘Preamp 4 (Tuner)’ before pressing Tuner on the front panel generates music.
I.e. looks like the label on the back on the 332 has this input labelled incorrectly