Robert Köpferl wrote:
  Be aware that it makes a difference  wether you have
got a so called
 multi serial card or  several plain old serial HW. I may be wrong, but
 isn't 4 the limit. Due to 'reserved' ports for that kind of HW?
 
It's a multi-serial card. The 4 limit for plain serial is due to
reserved/limited irq if I understand correctly.