Hi all, just finished rolling my own dual-tuner HD Myth box. Everything's working great using KnoppMyth R5F1, well after a bit of tweaking that is (ok, a lot of tweaking :)). I'm pretty happy with it now and just have one task that I'd like to finish - getting simultaneous analog/digital output from the onboard audio (Analog Device AD1986a using the Intel HD ALSA module - latest version, 1.0.14).

What I mean is that I'd like to either listen to stereo analog on my HDTV for news, documentaries, etc. but also have digital output sent to my receiver (AC3, DTS) whenever a show with 5.1 audio is playing. So, I could listen to either or both as I wish.
I've tried just about everything I can find on the net (like the custom multi-output .asoundrc on the Configuring Digital Sound mythwiki page) but can't seem to get it working. If I set the sound device to ALSA:analog instead of /dev/dsp and digital passthrough device to ALSA:spdif (or digital), I get no sound on the TV for analog shows with AC3 passthrough enabled. If I turn passthrough off, sound works fine but then no digital. If I set sound to ALSA:multi (using the custom .asoundrc), I get buffer underruns and audio/video skipping for all shows.

So best as I can tell, you can have all going to analog or all going to digital but not both. True or false?

I have my digi out sending all sound to my receiver, and most receivers these days switch on the fly between Dolby Digital/Stereo/Virtual Surround/etc depending on the source audio.

I thought about setting it up as you are thinking as well, but decided this would be easier to use in the long run (for turning the volume up and down from a universal remote set up to control multiple components at once). I know you can tell some programs to use a certain audio device, but I think Myth will only use one audio device for everything.

I think Myth will only use one audio device for everything.
That's not true. Once your hardware is setup correctly (in the OS via ALSA) it's controlled on the application level. I'm running MythTV (via an Ubuntu Feisty install) with the same motherboard as you. While listening to music via the MythTV audio player I get output from the analog 1/8 audio out jack as well as the S/PDIF optical out going into my stereo receiver. I picked up a cheapie 1/8 to RCA spliter from Radio Shack which I connect to my audio-in on the tv.

I have to add that I do have simultaneous output now to both analog and digital using the stock /dev/dsp device, but when I enable AC3 passthrough I get a helicopter noise (i.e. garbage) on the analog output, and digital works fine (i.e. I get DD on the receiver). What I want Myth to do is send the non-AC3 stuff to analog and the AC3 to digital, but it doesn't seem like that's possible.

Would Jack help in getting simlutaneous analog 2-channel and AC3/DTS passtrough?

Jack supports sending an audio stream to multiple processes (apps/outputs, I assume).

May take some serious hacking or tech-knowhow, but what needs to happen is to take the source audio stream, and duplcate it- one copy gets decoded and /or downmixed then output to the analog port, the other copy gets sent as-is to the SPDIF port.

I have a similar issue, in that I am trying to get my myth to use ONLY the digital out via (toslink cable) which works fine, then have the linux box use only the analog (via y splitter) out of the jack in back. Currently they both output at the same time. Anyone solve this yet?