Useful research Paolo, thanks!
I have a MOTU 828MkII and the MIDI drivers for that are multi-client, have no SysEx issues and are low in jitter according to MIDITest, so I’d be optimistic about the Express 128.
That will work perfectly and will introduce no jitter or delay as they are electrically directly connected, apart from optocoupler isolation at the input.
That will use up 4 USB ports, but there will be no power issues as each USB port can supply up to 500mA, which is more than enough for each of the EMUs. The cost of 3x 2x2’s will be very close to the Express 128, though …