With one box, you will be limited in the amount of processing you can do per channel, but you can sum them all (I mean you can mix them with level and pan).
That's because you are using USB. If you want to go up to 128 channels you need to use MHLink (Ethernet).
If you need more channels (but not as many as 128) and you are running at 44.1 or 48k, you can go up to 48 channels on USB by adjusting the USB channel count; if you run at up to 96k, you can increase it to 24 channels on USB. If you run at 192k, then 12 channels on USB is the limit.
The Round trip latency is slightly higher on Ethernet; but for doing mix down that should not be an issue. The lowest latency for live monitoring is by using the MIO Mixer, of course.