vFF.FF version is a special firmware,  to reset default setting, could not use for play. need upgrade a normal/hid version to use again after upgrade this special version.
It is used to solve the problem that some device can not display the sampling rate after upgraded v1.41 firmware.

Note: after upgrading the XMOS, it is necessary to replug (off then on) the power supply to enter the MCU upgrade mode, thus completing the entire upgrade process.

--Kenny 221230