Since the Saffire 6 does midi over USB, you should be able to use the midi in/midi out ports (they are 5-port DIN type connectors by the way) to connect something to the midi in on the saffire, provided the other gear you want to hook up has DIN connectors, which in the case of the F1/X1 they don’t.
DIN midi connections allow you to daisy chain. This is one MAJOR difference to Midi over USB. Most devices will have at least midi in, midi out and more often than not midi thru. So you can go from one machine to the next to the next.
The drawback to Midi over USB is that each USB device needs it own connection to the PC and usually it’s own driver.
The number of available ports need not be a big problem, a powered USB-hub should get you and easy 3-7 extra ports without a problem.
So, keep your macbook, buy a 20 euro high quality POWERED (important, or your stuff probably won’t function properly) USB-HUB and hook the sound card to one of your MBs USB port and the rest of your stuff to the USB hub and you should be good to go.
Greetinx,
C.