Tested now with 8 wired XBox360 controllers (just by myself octopus style) and it works!
Another detail: On my computer going fullscreen with Alt+Enter gives me a black screen.
By the way what's the current known record for 4 players? My kids and I haven't made it passed the U-shaped aliens at 123 seconds. Wondering if the increase in difficulty is a bit steep or if it's just that my kids are 4, 7 and 8 years old and can't give me the backup I need. ;-)