thanks
what I built was on-the-cheap. I had a spare metal cover from a network router - I inverted it and made a bottom/side chassis for it. (there is no top. its always in perma-tinker mode).
but for an on-the-proper build, see what my partner, Ti, did:
semi expensive metal work and fairly expensive front/rear panels (CNCd). all 8 ports are wired up (I only did a few on mine).
we measured these with audio test gear and the noise level and distortion was at our test gear level (130dB down at points). no 'arduino computer noise' coming thru at all thru the analog line (you can see 2 very visible ground plane separations on the motherboard; for analog and for digital).
I was worried about backlight (pwm) bleedthru, but again, our test gear shows this to be noiseless andn flat from dc thru about a mhz or so (well beyond audio needs).
what that thing is, btw: its an audio preamp that selects 4 inputs and routes to 4 outputs (all assignable to in or out); along with a 'stepped attenuator' volume control using relays, resistors and 256 steps of half-dB per step. the output of the attenuator board go into a pair of discrete (fet/bpl) buffer boards that give voltage gain and are nearly noiseless, with near zero output impedance. that would go to your power amp or set of amps.
you control it via a learning remote (arduino learns your remote) OR you twist the knob to change volume. if you use the IR remote, the knob is motorized and catches up (in the background) to the IR-set value. in this respect, whether you use the IR remote or the knob, itself, it always 'points the right way' due to the motor and arduino controlling it. ie, if you had used the IR remote to set the volume to halfway, then the knob will motor over to point to 50%.