Check out these and other music-related apps at Sweetwater here: http://www.sweetwater.com/shop/ios/apps.php
Mitch demonstrates Apple's Inter-App Audio functionality by using it to load Arturia's iSEM and Waldorf's Nave as virtual instruments within the Steinberg Cubasis DAW app. Check out the video, then get these and other music-related apps for your iPad at the link above!