It's not possible, the SX80 was released with TC7.1.1 software, even though there are TC software versions that are lower than that, you can't Use them with the SX80. This is because certain codecs have specific file versions and numbers that are used for that specific codec or series of codecs.
See the following discussion for more details, and use only the software files and versions that are listed in the download section for the device you have.
mx-800-downgrade-software-version
