I don't know where you might get the instrument definitions file for the Tyros (it will likely be a file called "tyros.ins"), but once you get it you put in the Program Files\Cakewalk\Sonar 2\Sample Content folder where you'll find other instrument definitions (assuming you chose to install them with Sonar). Also you should have the option to call up an OPT panel for the Tyros within Sonar for editing your voices. The OPT panel comes with the Tyros on one of it's program disks (maybe Tyros instrument definitions did too?).
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Jim Eshleman