FYI the MSD boxes such as the 6AL and similar, are all "CDI" boxes like Bryce was talking about.
That just means that products like the 6-series units are Capacitive Discharge Ignition modules.
And yes, the FiTech ECM can use the signal from the distributor alone to get the timing for the spark event. If you were running the distributor in question just as an ignition system without an external computer doing the dirty work, you would need the external module to do it.
One just takes the place of the other.
The reason it was also mentioned that "you can use an MSD box if you want to" is because some might already have them wired in to the setup and not want to remove it, or might not want to lose the other features that the MSD 6 offers. Such as multiple-sparks and rev-controllers.
You know... Stuff like that!;D
Paul