Not very familiar with Grains but… I mean, it’s an Arduino Nano, it’ll run the code, input pin assignments might have to be changed but that’s trivial. Question is the analog output. Synapse, the project dac/ino is based upon, was designed for control voltage output, not audio, and I have no idea if the DAC outputs are fast enough for what Grains is trying to do. Maybe you could use PWM — Grains writes PWM to pin 11 which is used in dac/ino to communicate with the DAC but if that can be changed to pin 6 or 9 those are available (one’s buffered and connected to a 2-pin Molex for an output jack, the other connects directly to a header or 8-pin Molex). Looks like Grains uses a hacky alternative to analogWrite and my guess is it can be made to work on pin 6 or 9 but I’m not sure. On Grains the PWM output is connected to a low pass filter, so doing it this way you’d probably want to bodge a resistor-capacitor network onto the output. Or not, the filter can be bypassed on Grains: “Bypassing the filter provides more clarity and a slightly louder output but more artifacts in the sound.”
Well, try it and report back!
Added: @sebastian was messing with a module that could run Grains sketches, apparently it worked but there were tuning issues. Probably a solvable problem. The hardware can be considerably simpler than dac/ino if it’s just running Grains.