nicegrin, my impression is that people here were talking about recording onto four separate channels from four microphones--then later, mixing those four signals down to two.
I use to do a lot of my 4 channel mixes onto DAT using a Wendt X4 ENG mixer. It wasn't until I bough the Deva 3.5 years ago that I started doing four+ channel mixes in post. The key is you have to use a mixer, have a nice set of headphones/earphones (I use the ER-4S when doing this), and realize that you can't put in any delay or fix any sort of issues, so you get one chance at it.
Wayne