This has been well documented especially on the newer model F-150's and other Ford models for being able to convert the ACM signal to a variable level pre-out for adding after market amplifiers. But for our model year the information has been lacking on even if it was possible or not.
I can confirm that this is possible on a 2012 F150 with Sony as I have performed this successfully. I was able to tap the Left & Right inputs from the ACM before the Sony amplifier and capture a clean full spectrum audio signal. The original signal from the ACM is un-processed fixed volume high level output. With a bit of programming in Forscan I was able to get this to a variable volume low level output in which I spliced RCA connectors to.

Currently the variables I have altered in Forscan have disabled some other features that I did not intend on losing, but I am tweaking variables to restore some of the functions lost while maintaining the variable pre-out. More information will come in regards to what variables these are.

Currently the functions that have been lost are:
No ability to Fade front/rear. (balance L/R works)
No sound output from rear speakers which remained on factory sony amp. Center channel is still working.
No Sirius XM tab on the radio screen. (Sirius Travel Link is still enabled and working)
No HD Radio tuning.
No Climate control through screen. (Does not show temp setting/fan speed and the Climate page does not open. Climate control is still working and is adjustable through analog buttons)
No Green/Yellow/Red squares with reverse camera. (camera still works and vehicle still beeps while reversing closer to objects). Volume of stereo does not dim when beeping kicks in.

Basically everything that has been lost with my current programming I would accept and be completely happy with what I have gained. The Climate control screen and HD radio are two things I would like to have back and will continue to tweak. I previously had integrated an aftermarket amplifier by using an Audiocontrol LCQ-1 and tapping the high level front speakers before feeding my amplifier which never obtained anything close to an acceptable aftermarket sound and required an excessive amount of wiring. Since doing this upgrade, the sound and clarity is exceptional and is a night and day difference to the previous integration. There is absolutely no noise, static, popping, etc and it is what you would expect from an aftermarket upgrade.

 

Did you follow this? This was for MFT and I think you have just regular ford sync so it might be a little different.

http://www.2gfusions.net/showthread.php?tid=3704

 

I followed the instructions and programmed the values provided in that thread originally but they did not work. I've got the 8" screen Sony system with USB and aux input. It is a 2012 FX4 with 505A equipment/ Sony Navigation Radio and FX Luxury package.