Here is a summary of the method I posted earlier, with some minor modifications. Good luck. THIS IS ONLY FOR ADDING ROCKBOX PORT TO NEW 770C (post 6/2016 model)....
OK, I have now spent quite a bit of time playing around with the firmware upgrade process to Rockbox the new 770C. The method is much simpler than I previously realized and works well with both Windows XP and Windows 7 (still does not work with Windows 8 or 10 as far as I know). In any event, you will still need to download the "ihifiupimg.rar" file from the Xuelin site if you have not already downloaded the drivers onto your computer. Here is the link to this file:
http://pan.baidu.com/s/1hreOzti?qq-pf-to=pcqq.c2c (click on the box with down arrow 11.3M to download file). Once you have used the Release_driver assistant to download the drivers onto your computer, then download the rockbox-bootloader file from XVortex onto your computer. Here is the link: https://mega.nz/#!MstEVZDY!xUTJEINqfLgAmC66kLy-EvbuSyQ7kqDCUDe_JcjnYLw. After you have downloaded this file, then download the Rockbox-full file (https://mega.nz/#!whsABBxY!EO0q_nkR-Jc0th8aAs7TOD7E1ViOEtRFW1-VPppM7-Q) to your computer. When you open the rockbox-full file, you will see a file named .rockbox. You will need to extract this .rockbox file to a FAT32 formatted microsd card. Once you have extracted the .rockbox file to your microsd card (make sure to check the card to see if .rockbox is there), the copy the update file (https://mega.nz/#!ot0gla5b!ue0Fi5Gq-fTsWX5uWRotpTaz2172Q-p8WJfOYHfinzc) to your microsd card. Once you have the updated .rockbox on your microsd card, then place the microsd card into the slot in the 770C. Now attach your 770C to your computer with its usb cable, the 770c screen should show the usb symbol on the left side of the screen and a headphone image on the right side. Now open the rockbox-bootloader file and locate the RK27 upgrade image; click on this and the upgrade image will appear on your screen. If this is the first time you have used the upgrade image, you may need to run it as administrator. After the image opens, the bottom left text box should say something like "Found RK27 MSC Device". The image path (near the middle of the image) should already contain the text that reads "Image\770c-rockbox.img" (or something similar). So next, you will click on the Upgrade button located just above the Image path. A pop-up may appear that says "Device don't support, upgrade failed". If this happens, click OK on the pop-up and the pop-up will disappear. Next click on the Switch button (next to the Upgrade button), the text box in the lower left should now say "Found RK27 Loader Device". Now click on the Upgrade button again and the firmware download should begin. You should see lines of text appear in the large text box in the middle of the upgrade image. When the process is complete, there will be 13 lines of text, the final one says "INFO: Upgrade OK". The 770C will then turn off briefly, but then should automatically reboot. If it does not reboot, then do a hard reset and then turn the player on with the power button. This next part may or may not be true for the new 770C firmware, so you may need to wrk this part out by trial and error: When you disconnect the 770C from the usb cable, the screen on the 770c will have the Xuelin firmware still showing in Chinese. There will be 5 lines below the battery icon, move to the bottom line and press select key. The 770c will then go thru an uploading process and a new screen will appear also in Chinese. On this screen, there will be 6 lines below the battery icon. Move down to the 6th line and press select. This will open a screen that will let you select the language you want to use. Move to the language you want and hit the select button. You can then use the return button to move back to the main screen. To get to Rockbox, simply push the power button to turn off the player, then use the power button to turn the 770C back on. The Rockbox screen will appear when the 770C is restarted. Remember, you have to have the microsd card with the .rockbox file extracted to it in the microsd slot to access Rockbox on your 770C.
I hope this work out for you. I'll try to answer questions, if you need help....
