Hey guys, new guy here.

I have a Pro 40 as my main, i've been using the 11rack for my guitars and bass but never used re-amping, now i think that it would be very useful but i don't know how to re-amp into Logic X.

Also, i know there is a way to do it using S/PDIF but i don't have them right now...

Can you tell me how many methods there are, how to do it, which is best and why?

This will tell you how to do it (written for reaper but applies to logic x also):

Eleven Rack Reamping

I don't have any experience or specific instructions for the saffire pro 40, but the instructions are assuming you would be using the 11r for the interface. If you need to use both interfaces at the same time (and you are on a mac) you can set up an aggregate group through the mac app 'audioMidi setup' (combining both interfaces to be used together). I have done that with my 11r and my duet2 but it gets buggy sometimes and I delete and re-make it to fix when it happens. I hope this helps.