HI Guys:
Here is the newest stock firmware for T-r42 also called MK888B quad core TV BOX. T-r42 is the upgrade model of K-R42, it built in bluetooth.
Here is the stock firmware download link:
http://www.mediafire.com/download/2tf3pgwvla4d9tw/T-R42_New_stock_firmware_0928_By_Geekbuying.zip
Firmware upgrade instruction,you can check here:
https://blog.geekbuying.com/index.php/2013/10/14/stock-firmware-for-t-r42-quad-core-tv-box-with-bluetooth-function-flash-method/#.UoBL9OIo8r0
Enjoy!
Eric
Geekbuying