This is a very Deep Topic !! my English not enough to explain..i can write just small tips
My setup is ; Audya and VoiceLive 2
TIP 1;
On my Audia; i put vocal track to channel 16 for midi files (make volume 0)
from Voice live setup; Adjust midi in track to 16
in voice live; create a patch and use "midi notes" option from harmony menu if you have spacial harmony track
connect from midi out audya to midi in voice live
play a midi file and sing a song
TIP 2;
For live play with styles via midi connection;
in audya midi setup menu, open channel tx menu and give channel number 16 to left (f2)
in voice live you can use any patch you want with this setup
TIP 3;
For live play with styles or midifles; you can use a easy connection;
in audya midi setup channel tx menu make off all channels or don't use a midi cable
connect From audya headphone out to voice live AUX in (mini jack)
play and sing
Regards
Necdet Doni