The Tyros 3's only expansion capabilities that I know of are loading Yamaha proprietary voice files (which I don't believe are available yet) and installing a larger hard drive. Loading third party samples into any Yamaha keyboard is a waste of time unless you don't mind waiting a long, long, long time.

The Korg is expandable and can load third party samples which is a big plus. The Audya can also load samples so in respect to expandability, the Audya and Korg win out over the Tyros 3.