Indeed, so there is a safety function on ODrive to stay inside its configured current range, and not suddenly apply 9V, ie its minimum supply voltage, to the motor. You will have to validate/certify this requirement yourself, since ODrive is not a safety certified product.
But depending on what your external protections are (100mA fuses would be a good start - I was thinking also zeners, but they could confuse the current controller), it might be possible to say that the ODrive cannot blow them if you power it from 9V DC, for example.
I have ‘used’ the S700. (tried it, alongside drives from Elmo, Copley and Moog, and eventually sent the S700 back to Kollmorgen. It is a very big and loud machine (but yet still uses PWM so I believe) that must be powered from at least 110VAC (200V DC Bus) but ideally wants 415V mains (600V DC Bus). The front-end X/Y capacitors are so big that they will trip most RCDs.
I think they will struggle to run a motor at 2V 100mA.
Also they trumpet a lot about functional safety, but i’m not sure if they will certify anything that is not a Kollmorgen motor from their catalogue, with a Kollmorgen encoder. And all that will set you back about 10-20k per axis.
That could work, but would involve a LOT of software (firmware) redevelopment, since the ODrive is very much a PWM controller.
I wonder: If you replaced each phase output with a capacitor to ground, (i.e. turn it into a DAC) and wired it from there into a linear amp, it might work.
You would need to move the current shunts to the real output and perhaps add your own amplifier…