Adding VU meters to an Aikido OTL headphone amp.

I'm in the process of building an Aikido OTL headphone amp and thinking of add a pair of VU meters, just for the look.

The driver board I intend to use is this one: https://www.ebay.com/itm/1668490787...HbusGwtRI-&var=&widget_ver=artemis&media=COPY

My question is whether I should connect the meters to the RCA input (fed from a 2Vrms output DAC) or headphone output?
And of course, most common question, does these meters affect the sound in any way?

Thank you in advance.

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Take the RCA input, it is neutral. The volume potentiometer influences the display on the headphone output. Apart from being a nice, optical gimmick on a headphone amplifier, such displays have no other useful value.