How would you add remote digital control to an analog mixer and headphone amp without fully redesigning the circuit?

Hi everyone,

I am looking for ideas on how to digitalize part of my audio setup so I can control it remotely, but without doing a very invasive mod or something too hard to replicate later.

Right now I use two simple devices that work well:

\- an MX600 6x1 audio mixer

\- an HA400 1x4 headphone amp

My goal is to remove these boxes from my desk to reduce clutter, and leave only the controls on the desk, or maybe control everything from a PC using some software made by me.

What I want is:

\- remote volume control per channel

\- if possible, keep the original knobs working locally

\- simple, cheap, and easy to replicate modifications

\- something that does not change the original circuit too much

\- if possible, mute and unmute per channel too

I opened both devices and identified some ICs on the boards:

\- mixer: JRC 4580 and KA2284

\- amp: HT4560

From what I understand so far, the 4580 and 4560 are the actual audio op-amps that matter here, while the KA2284 seems to be related more to level indication and not the main audio path.

My main idea is to reuse as much of the original circuit as possible instead of redesigning everything from scratch. I would prefer adding remote control around the original analog design rather than replacing the whole audio stage with something completely different.

Some approaches I have considered:

\- stepper motor or servo attached to the original knobs

\- replacing the original potentiometers with digital potentiometers

\- replacing the knobs with rotary encoders and controlling volume digitally

\- doing some small modification around the original circuit to add remote volume and mute

One idea I have been considering is using a simple and cheap stereo digipot before the original analog potentiometers, either in series or as some kind of input attenuation stage before the original pot, so I could get a coarse remote volume control without losing the local manual adjustment. That way, the original pot would still be there for normal use, and the digipot would act like a remote pre-control. I also thought this might help me add some kind of mute function.

At the same time, I do not want to ruin the original behavior of the circuit, degrade audio quality too much, or create a mod that is annoying to maintain. I want something simple, functional, cheap, and easy to reproduce. If one of these devices dies in the future, I want to be able to rebuild the mod without too much effort.

So I would like to hear opinions from people who have done something similar or know a better approach.

What would you do in this case?

\- Would you try to reuse the existing ICs and original circuit to add remote control and mute?

\- Would you put a digipot before the original potentiometer?

\- Would you just use motors on the knobs?

\- Or would you skip modding altogether and buy another mixer or amp that already has remote or digital control?

Any practical, low cost, and easy to replicate ideas would be very welcome.