If you are looking for the latest Android 6.0.1 Marshmallow stock firmware for your T-Mobile Galaxy S6, you can grab this stock firmware ending in “PF1”.
There are many versions of Android 6.0.1 Marshmallow but this is the latest one and you can install on any T-Mobile Galaxy S6.
Latest versions upgrades your bootloader, modem, and system to the latest PF1 stock firmware. Rooting is very easy, simply follow the S6 Root Guide.
For installation, please refer to Galaxy S6 Unroot Guide. You will need a Windows computer and ODIN to flash this stock firmware.