you can not connect them in chain such as scarlett->modi->magni and could only use modi->magni or scarlett->magni as the modi/scarlett are basically the dac portion.
you could use a scarlett just for mic input but that may be a waste over using a smaller, cheaper, simpler single input xlr mic interface or just using a 48v supply with adapter. if you used the scarlett as the dac then the modi would not be needed unless you decided to keep it for when you are not streaming or recording.
there is a usb version of the 2020 as well (though if you intend to listen to your voice live, this is not the way you likely want to go).
basically you need to make a choice:
A) i want to listen to my voice as i record! use the scarlett and just sit the modi on the shelf when you record.
B) i dont need to live monitor my voice! keep using the modi and magni and either use a usb mic, an interface for mic only or a 48v adapter alone.