Well, I am using one Steinberg Midex8 with a couple of old JLCooper MIDI patch-bays (a 16/20 and one which is 8/10 and has manual routing knobs for each MIDI input). I don’t know what your definition of a “larger MIDI rig” is, but I’ve got some MIDI keyboards and rack modules (enough to fill up the path-bays and there are still some unused devices). I’ve used Cubase since before it was called Cubase, on Atari.
BTW, I am not sure that two Midex8’s can be used together on one computer. I read somewhere (in the forum here) that people have had problems with setups involving more than one Midex8 device. So I would check with the forum and perhaps with Steinberg Support before committing, if this functionality is important.