I have been getting some emails asking for firmware update information. Here is the info that I have at the moment.
There will likely be several concurrent firmware development tracks in further development, including one that is being considered by independent Rockbox developers.
The best firmware for your T6/Rocker is likely going to be the one provided by the company that sold you their product, simply because it will be supported by that vendor in case you have an issue - Shenzhen Benjie in China and AGPtek in the rest of the world as it stands right now.
At some point in the future, Rockbox developers may release their version in conjunction with AGPtek or they might just do an independent release. For now the two or three developers involved are talking to each other as well as AGPtek. At least one Rockbox developer has now said he will do a "Rockbox as an app" port using the Linux kernel of the T6/Rocker.
As of February 23, 2017 there are two released and installed retail firmware versions that I am familiar with. Both enable full functionality of the T6/Rocker but there might be some subtle branding, menu and functionality differences that I am not in a position to compare side-by-side for a couple of weeks yet. No worries, both versions are fully functional firmwares that support the full range of file compatibility of the DAP.
AGPtek has their V.1.01Beta currently installed on the Rocker for international distribution and Benjie has their V1.04Beta, which was made available to me and which may or may not be sold in their Chinese distribution. I do not know if the Benjie version is, in fact, a later developed version but I received it on February 7, 2017.
Please note that the use of the word "Beta" in the naming scheme does not mean you have a pre-retail release version of the firmware. The use of the word "Beta" means that AGPtek/Benjie intends to continue firmware development and refinement coding is still in process until the device reaches end of life in the product cycle. At some point the firmware will likely not include the word Beta, meaning that further firmware coding is no longer in process by Benjie or AGPtek.
In comparison, the pre-release firmware version was simply named V1.0 and identified the device as a K1, the manufacturer's working model nomenclature. You can see this in the photos I have in the first post of this thread. If you somehow have a V1.0 firmware installed on your T6/Rocker, then you really should do a firmware update to access the full range of file formats the DAP is capable of playing, as well as some language/menu enhancements.
Firmware updating on the T6/Rocker is super easy but you should have a copy of your original firmware to revert to in case your update fails. Don't call me if any updating or change doesn't work or you brick your DAP, I am not being paid to support your experimentation.
To update, just copy the update.upt file you have onto a properly formatted microSD card, insert the card into your powered off DAP, power it on, go to the Settings Menu, scroll to Firmware Update and then activate the Firmware Update function. It will take a minute or so and then the DAP will power off and then power on again with the new firmware installed.
I am not able to attach a copy of the update.upt V1.04Beta firmware file I have in hand, looks like the forum system does not recognize the file format or it is blocked (not a valid JSON object?). Will attach if I can figure out a workaround.