Do you know what exactly is different, by chance?
I don't know spec-wise what's different since I've already committed to going with the Parrot Asteroid I posted about earlier in the thread.
I've done a little more detective work on this and have the following to share.
These 3 images came from subaru.com
Forester h/k setup (FM612US) found in the higher trim levels. Presumably (based on the audio system info in the "Everything you ever wanted to know" video) this is the same thing as the STI's h/k and navigation combo:
BRZ Premium level setup (FA601US), which appears to have the same control hardware as the Forester's k/k, but obviously is missing whatever special stuff the h/k package brings along. Perhaps the nav portion of the BRZ is indeed the same as in the Forester.
Base audio from a 2014 Impreza (CM621UB) which presumably will be the same as base audio in WRX/STI
This image of the WRX navigation unit, which does not have h/k included (FV619US) was found online:
So, between the Forester with h/k and nav, and the BRZ and WRX with nav but no h/k, we have three different part numbers. What this really means, outside of the obvious difference for the h/k unit, isn't exactly clear from the pics alone. I'm not interested enough in the topic to dig into spec sheets, but now that the part numbers are known, perhaps someone else will take that one up.
*edit*
The base audio for STi will be the CV629UM