Audio not working on Yamaha CRX-332

[FD-]

I'm trying to use your great project on a Raspberry Pi Zero for adding AirPlay support to a Yamaha CRX-332 stereo system that supports iPod connections via USB.

Unfortunately though, I cannot seem to get it to work. Although the devices seem to perform some iAP handshake and I cannot find any obvious error reports, speaker-test doesn't work, failing with Write error: -5,Input/output error after a few seconds:

pi@raspberrypi:~ $ speaker-test -D plughw:CARD=iPodUSB,DEV=0 -c 2 -r 44100

speaker-test 1.1.8

Playback device is plughw:CARD=iPodUSB,DEV=0
Stream parameters are 44100Hz, S16_LE, 2 channels
Using 16 octaves of pink noise
Rate set to 44100Hz (requested 44100Hz)
Buffer size range from 92 to 16384
Period size range from 23 to 1024
Using max buffer size 16384
Periods = 4
was set period_size = 1024
was set buffer_size = 16384
 0 - Front Left
Write error: -5,Input/output error
xrun_recovery failed: -5,Input/output error
Transfer failed: Input/output error

My trace file can be found here: ipod.trace.zip

Does anyone have an idea what might be going wrong? Any help is highly appreciated!