I do this. I currently have a Komplete Audio 6, which has four analogue ins, and a couple of the Roland AIRA fx I picked up cheap and also act as audio ins. This works fine.
However, I am currently debating with my GAS around getting a MOTU 828es, which looks very appealing, and has some native fx on the way in.
The K-Mix looks good too, I guess for my needs I don’t really need an outboard mixer, the functionality looks a bit menu-y, and if I want to control levels live, I can simply do it in the modular itself. But I’ve definitely thought long and hard about that one too.