Hi, good question. “Lucky” me, my crowdfunding purchases keep delaying so I still can use my Evo 16 without an expansion. I am also wondering what to buy if and when the new synths arrive, since I will need more ports.
The Audiofuse 16 is newer and therefore triggers extra GAS on me the days I feel weak. It has more control possibilities when disconnected from a PC, which is a useful feature for Linux users like me. But yeah, it is more expensive and it has many more features that, well, I won’t need.
The Evo16 is working well for me. Once I fined tune the settings with a PC, it does what I need when connected and standalone. It offers the flexibility I need and more (I’m not using talkback or the digital inputs). Although in theory line inputs are enough for synths, I am making good use of the gain available in the Evo16 inputs. I find their quick automatic calibration of gain is convenient too.
For these reasons, if I had to decide today, I would go for the SP8 expansion instead of selling the Evo16 and buying the Audiofuse 16. But I don’t have to decide yet, so I keep reading topics like this one just in case. 
PS: just for documentation purposes: