You could buy a Folcrom summing box. They're relatively cheap. You can then do your summing in the analog domain and use one of your mic pre's for the make-up.
I don't recall if the units you mentioned come with DI's, but if they do you can send stuff out of your digi into a reamp box, then into your fav guitar pedals, then use the your DI to get back into the digi.
I can't really see how else you're gonna use your mic pres during mixing except if you re-amp stuff live.
Hope this helps,