I am curious why one would want EQ saved settings by source. Is anyone really going to use a different EQ for, say AirPlay vs. Bluetooth vs. a turntable/phono preamp? I guess the lattermost might make sense if the phono preamp was a poorly-designed unit with no available rumble filter, but otherwise not sure what the use case is here.
It seems to me it makes a lot more sense to have EQ saved settings by output. The use case here is, for example, a system that is connected to two separate transducers: loudspeakers (via the analog outputs) and headphones (via a headphone DAC/amp connected to the digital output). Then you could listen to headphones with EQ, but switch over to your loudspeakers seamlessly rather than coloring them with your headphone EQ.