With an Apex-i S-AFC alone you CANNOT even get close to the same results that you would get with the AccessProt.
The S-AFC is just a piggyback computer that controls air-flow. It intercepts the ECU signal and modifies it based on what you or someone else has specified.
I had the S-AFC v1 on my old car (2000 Celica GT-S) and it was absolutely useless, short of looking cool. Don't even ask me why I got it (fortunately I was able to sell it on eBay for $50 less than what I bought if for). The only way I could get any power out of it was to have it lean out my fuel mixture. But I didn't really want to do that since it would've greatly increased my chances of detonation.
The AccessPort will basically reflash your ECU and can modify settings far above and beyond basic fuel and air delivery and more importantly make everything work together. The Cobb website does a great job of giving a simple explanation about the AP, so you might want to check that out.
With the S-AFC you can pretty much modify your air/fuel mixture on the fly (for different RPMs, throttle positions, etc.) but that's the only advantage that it will give you. With he AccessPort you can load different maps to your ECU on the fly but cannot actually change any of the settings in those maps (and you actually wouldn't want to unless you really knew what you were doing). You get the maps from Cobb’s website, load them on the AccessProt device and then upload them to your ECU. The device can store up to 10 maps at any time. There are other advantages to the AP as well.
I am not saying that the S-AFC is completely useless, there are cases where it will be very useful, but in this case it will not provide any advantage.
I don't know if any of this makes sense but I'd say definately get the AccessPort!

 

Good choice!
I am actually thinking about getting the AccessPort at some point (don't have the money right now ).
Just as a side note, if you have an 04 WRX, there have been some rumors going around about people running lean from Cobb reflashes. I don't think that any of those have been substantiated yet (running lean can be caused by many things) but, it's just something to be aware of.

 

As my previous post says, I don't think that any of the lean condition claims have been substantiated yet. And I don't know if the people had any other mods on their cars.
I haven't really researched any of that though or know any of the details. Just stuff I've read.
My personal oppinion is that the lean condition was caused by a factor other than the ECU reflash.