Yup, 48k 24 bit is fine, just make sure that everything's set that way!
Firstly, you'll want to create a new scene for playback, as it takes quite a lot of set up to get it working, and it
disables live signals from being passed through the desk. When you recall another scene, everything goes back to normal though, so don't panic!
I'll double check this tomorrow, but from memory: firstly, have your new scene recalled, and the mac set up, ready for playback, with the virtual soundcard enabled. Select the first channel and go to 'preamp' on the touchscreen (it'll be in the list along with gate, PEQ, comp etc). At the top of the preamp screen, there should be a small drop-down menu with 'IDR mix rack' selected. Change this to 'Dante virtual soundcard'. AFAIK the channel number and other details don't need to change. Once you press 'Apply', the channel will now listen to the mac's playback of the corresponding channel, rather than that input on the mixrack.
Unfortuantely, you have to do this to every channel that you want to play back, but once you've done it 48 times, you can save it and (in theory) shouldn't have to do it again!
Just to reiterate: once you change the channel to from 'mixrack' 'virtual soundcard', any signal sent into that input of the mixrack will be ignored, so be careful!
I'll double check all this tomorrow, and post back if I've said anything that's not quite accurate.
Hope that helps!
Joe