I have been using the Synthmaster Player for iOS for quite a while already. You still get to hear the basic amazing sound of Synthmatser. The pro version of the player ($9.99) unlocks a whole lot of features and you can edit sounds quite extensively. It sounds stellar and is one of the best sounding synths on my iPad currently.
I have my iPad docked into an Alesis I/O Dock II which provides a quality D to A sound at + 4 dBu balanced. It sounds excellent and the latency is excellent as well.
This latest version will unlock most of the full version of Synthmaster for iOS. It might even include the latest wave table additions etc.. It will be worth having if you run an iPad.