This zipped archive includes version 3.0 Operating System and Preset Objects for the PC2 Polyphony Expansion option. You only need this file if you have the Polyphony Expansion option installed in your PC2 series instrument. 

In addition to installing this file, if you don't already have version 3 installed your unit, you will need to download and install either:

PC2COMB310.ZIP for a PC2 76 note keyboard
PC2XCOMB310.ZIP for a PC2X 88 note keyboard
PC2RCOMB310.ZIP for a PC2R rack

Please note that while the current version for the main engine board is 3.10, the current version for the polyphony expansion is 3.00

Please see the README text file included in one of those files, for details on how to install those files as well as the polyphony expansion file.
