the card that you're looking at does have stereo analogue out, AND headphone jack AND s/pdif out AND has an internal software routing system that is FAR superior to anything that i have seen before... so you're golden, using the ADAT's for a/d converters works out really well, they sound great with the RME... for monitoring, just take the stereo out to your amp and volia... you can hear what your doing...OR as you said you can rout it back into your board so you can finish the mix there, it's up to you...
cheers