Since getting the ot everything to me is a sample source! I also have bought a crap load of apps and haven’t finished a damn thing with it and to be honest I don’t think you can.'at the moment
Apps like animoog though are as good as anything in the ios sphere or vst in general. It’s bloody fantastic.
Samplr is pretty good but you have to be disciplined or you’ll end up noodling for hours with little to show for it.
I haven’t been able to get into lemur which is a shame because way back in the day I almost bought one
Sunrizer has a great synth engine
Thor is deep and my second fave after animoog
Check out boarderland s - lots of cool potential for sample fodder