[linux-audio-user] how enabling non-audio (AC3, DTS, MP3) S/PDIF out at ALSA?

Hi everybody, I would like to know how I could enable the use of non-audio (AC3, DTS, MP3) S/PDIF out at the ALSA context, in a set-top-box with the ALC650 AC'97 chipset, without having to re-compile the Linux kernel. In the linux-2.6.13 kernel, in line 1733 of the the source code "sound/pci/ac97/ac97_patch.c", there is a function: "patch_alc650(ac97_t * ac97)". In this funcion, several ALC650 registers are read and written. I know that, for enabling non-audio (AC3, DTS, MP3) S/PDIF out in an AC'97 chipset, I have to put a "1" at the 2nd LSB bit of the MX3A register, and also choose the correct Category Code for the non-audio S/PDIF format (AC3, DTS or MP3). So I have to basic problems to solve: 1. Find out how to create an AC'97 instance (ac97_t * ac97), in order to use the function "void snd_ac97_write_cache(ac97_t *ac97, unsigned short reg, unsigned short value)" for writing in the MX3A register; 2. Find out the correct Category Code for each non-audio S/PDIF format (AC3, DTS or MP3). If someone could help me, I would be very grateful. Best, Francisco