[OT] help with mplayer option to replicate aplay -D option

[Gianluca Cecchi]

Hello,
I have a system based on Asus M4A785TD-V EVO mainboard that comes with
VIA VT1708S chip.
On this system I have both F11 x86_64 and F12 x86_64.
I'm trying to have dts streams working through optical plug that the mb has.

Some progress from F11 to F12, probably due to the alsa version into the kernel
(2.6.31.9-174.fc12 vs 2.6.30.10-105.fc11).
I formerly found another thread opened in 2009 in alsa-user or
alsa-devel where this command was referred as working through optical:

aplay -D iec958:CARD=SB dts_file.wav

- In my F11 this command gives no signal through the receiver

- But now in my F12 this commands succeeds!

My receiver has:
3 leds controlled by a button named "mode": digital, pro logic, st

3 leds controlled by a button named "input": line, optical, coaxial

When I set input button to optical and play the sample dts file with
the command above in F12, the mode led automatically switches to
digital, and a led named "lock" blinks and I get sound through
optical... hurra!
Also, the other leds referring the 5 channels switch on and I hear the
sound through all of the 5 speakers
This works even if pulseaudio is running, so that it is not the
problem.... (I suspected this when testing in F11)

Now the help required at this point: mplayer

I'm using the one provided by rpmfusion free repo
mplayer-1.0-0.111.20091029svn.fc12.x86_64

mplayer -ao alsa:spdif with a dts sample file gives no sound in F11
while it "almost" works in F12.
I use almost because when I play the same file as before, the mode led
doesn't go to "digital", but to "st".
I can then press the mode button having it switch to "pro logic" and
again to "st", but not to "digital"
And the sound is not the same as with the aplay command.

Is there an option to give to mplayer to have it use the device that
in aplay is "iec958:CARD=SB"?
It seems I didn't find the right combination.
Or if it is possible to create an entry to add in asound.conf like

pcm.viaspdif {
 something
}

and use then mplayer with a commad such as

mplayer -ao alsa:viaspdif

Thanks in advance to anyone available to give any light....

Gianluca