Unfortunately, there are no Mac equivalents to the iPad Smart Instruments as the Mac obviously does not have a touch sensitive screen.
The software instruments on the Mac are therefore standard midi instruments.
Therefore any instrument iPad Smart instrument that goes to the Mac is converted into a standard midi instrument, so when it returns to the iPad it is no longer smart and cannot be substituted for another smart instrument.
As I show in this video:
http://www.youtube.com/watch?v=jHNRILXGEH4
If you create anything using the standard Mac Software instruments and export it to the iPad it shows exactly what it is but plays as a piano on the iPad as shown in my video.
What I have done with the fixed1t instruments is modify a set of iPad instruments so they are polyphonic standard midi instruments on the Mac.
Therefore when they are moved back to the iPad they play the sound they are supposed to.
But....
They are no longer smart instruments..
and they show as standard piano instruments, but if you play the piano keys they are in fact still the same sounding instrument but playing from piano keys. This means that you can continue to work on they and have the sound you want.
I hope this clarifies things.
fixed1t