Mixing with the whole mix running?

[RedDog]

One thing that can't be emphasized enough, is to use only one speaker for it. Don't just flip the mono switch from the DAW, make sure the sound is only coming from one speaker. It was quite a light bulb-moment to realise, why all those old hags and bearded bastards had three speakers on their desk instead of two.

You'd think that it would be quite self-evident but I know I have made that mistake earlier.

Great tip! Phase cancellations are a huge factor even when mono'ing from 2 sources, I don't know if many people realize that.