Got a new OTG cable and same issue. I noticed that, once the cable was plugged in, even without kernel module and USB mouse, Kindle toggled between host&gadget mode, however USB audio works....
Upon checking I found sth. interesting in arch/arm/mach-mx6/usb_dr.c(complied to fsl_otg_arc.ko)
Code:
int audio_enumerated;
EXPORT_SYMBOL(audio_enumerated);
and audio_enumerated is defined as an extern int in sound/usb/card.c. Changing it to 1(and comment out the EXPORT_SYMBOL line) should bypass the audio card check and make host mode working with other devices. Maybe there're other checks but I didn't dig further. However "rmmod fsl_otg_arc" crashed my PW3, as I don't have serial on it, I didn't try to replace it on rootfs. And, with a USB hub, connecting both USB audio card and mouse might get mouse working.
TL;DR: Find some hidden check in kernel source but can't test it.