You should be able to get rid of the output of the libraries by piping stderr away
cvlc -q mymedia 2> /dev/null
As for the commands, I'm not sure vlc accepts commands from plain stdin, but it sounds like the rc interface might be what you're looking for.
cvlc -q -Irc mymedia 2> /dev/null
You either need hw:1,0 (pure hardware device) or plughw:1,0 (standard plugin for resampling in front of hardware device) as ALSA device name for your card 1 subdevice 0, or you can do aplay -L and have a look at all standard device names (which will include channel selection and more)
As the synology uses a non-standard linux environment and CPU architecture, it isn't as simple as dropping a binary on the box. However, vlc can be installed via optware on the synology, which is (relatively) simple to setup. You can see that vlc is available in optware here: http://ipkg.nslu2-linux.org/feeds/optware/cs08q1armel/cross/unstable/
To setup ...
Because the device name is front; the CARD=SB,DEV=0 part is telling you which device it corresponds to.
You you need to do something like alsa-audio-device=front.
VLC, at least in my testing, will take either front or front:CARD=SB,DEV=0. However, it will error out if the device isn't actually usable. E.g., aplay -L will happily list HDMI ports with ...
Clear out your old VLC using synaptic package manager.
Now sign into Software Manager by pressing Menu and use
Top left software manager and insert your password
Search for VLC and press enter and allow linux to load it.