The 3312 and 3313 are different in several respects. Here is one that is crucial for me. The 3312 has a button that allows control of individual channel levels. The 3313 does not. Apparently with the 3313 you are at the mercy of Audigy. I have a classic Klipsch setup - two Klipschorns and a Belle Klipsch for the center channel. Control of the center channel level is absolutely necessary for adjusting the 'hole in the middle'.
The 3312 also allows the front panel switching to operate in standby - great for watching TV. The 3313 does not appear to have that feature. So you get to heat your house when watching TV shows.
I wanted to be prepared for 4k, but these are deal killers for me.