Beagleboard Rev B U-Boot audio validation is mono only

Maybe someone remembers that the U-Boot 1.3.3 of the Beagleboard Rev B
apparently does some audio validation test. At least according to the description

It prints "Audio Tone on Speakers ... complete".

I have found the source code within

and it programs the TPS65950/TWL4030 through I2C and initializes
McBSP2. Finally it sends a data block to the McBSP.

The code is also found in this patch:

(search for 'void audio_init()').

I have now added this to my own U-Boot code and did run it on a
BB C4 and our own OMAP3530 hardware. But I only see sound on
the HSOR channel. Although the code appears to initialize HSOL
as well. I also tried to enable the EAR amplifier but it can only
output the left channel and therefore I have a constant bias level
but no signal.

Has anyone experimented with that? And remembers any ideas?

Hints where to look at? McBSP programming? Or is the
code Mono only?

As side questions two probably unrelated issues I don't understand:
a) why does the code program VAUX3 and
b) does write to the MCBSPLP_REV_REG which is read only.

Many thanks,
Nikolaus Schaller