ADAT to computer

[wordhart]

The ADAT/Edit card is supposedly "sample accurate". I want to record on ADAT XTs and an XT-20, then sometimes transfer to computer in order to edit tracks and tune vocals, then either transfer back to ADAT for mix-down, or maybe mix on computer using some big-time software like cakewalk....
1. If I stay with my analog mixdown, can I use ADAT/Edit to edit and TUNE selected tracks?
2. If I use some more powerful software, can I stay within the digital 16-bit (XT) or 20-bit (XT-20) realm on it, without further conversion or "dithering"? In other words, do these mixing softwares REALLY receive ADAT digital, or do they muck with it???