unfortunatly in the realms of software theres not a whole lot you can do. the problem is that when working on a real desk each channel will add non-linearities and move the phase slightly.

the closest thing we have in the software world at the moment is nebula which employs an advanced version of dynamic impulse responses. the virtual console libraries are quite good and add a little depth and clarity that no static plugin can.

although by all accounts this is about to change with the steven slate virtual console plugin which differs slightly with each additional plugin which you add to the session.

to be honest, without spending silly money on a big old analog desk, the best thing you can do is invest in a small quality desk and send your mix groups out thru it and record back into your DAW.