First, back-up the current firmware and EEPROM files with the Flash and EEPROM utilities, respectively, found here. Be sure to save the files and not misplace/lose them.
If you want to use an iHAS220 firmware, then you will need to crossflash using the Flash Utility and the stock, unscrambled firmware found here.
Afterwards, if you want to play around with some patched firmwares, you can find them here.
Lastly, if you crossflash your drive, you will lose the warranty on it. Something you may need to consider if that’s important to you.