I’m not sure if these are exactly what you want, but I would suggest looking into Noise Engineering’s Vice Virga and WMD’s Sequential Switch Matrix as potential ways to get to where you want.
EDIT: Have you considered an arpeggiator that allows you to step through arpeggios with triggers? Shakmat Modular’s Bard Quartet accommodates four independent channels of this (the quantizer in for each channel becomes a trigger in). You can set the scale and arpeggiator pattern independently for each channel. It is also quite easy to switch between saved scales and edit the current one. Each channel can alternatively be used as a quantizer as well with the possibility of changing notes with a trigger at the gate in, which can be turned on or off for each channel.
I know this isn’t exactly what you were looking for, but perhaps you could get similar results, depending on what you’re going for.
There is also ADDAC System’s Intuitive Quantizer that allows you to trigger note changes for each of the four channels completely independently, but it doesn’t have many of the other nice features and UI that the Bard has.
I’m thinking mix your signals together (and adjust to taste at will), feed them into the quantizer, then trigger the note changes with the quantizer.