What the error saids. Your sound card is busy playing sound with an unknown sound program. Some sound cards have software mixing, so you have to use ALSA dmixer to mix all sources together to one device. For the flash player not outputting any sound, again the sound card is in use with an another program. The flash player outputs its audio to OSS, so you have to use aoss. Read ALSA documentation about asoundrc file.
I know that VIA soundcards can be pretty finicky about using a generic driver...
My Audiotrak Prodigy 7.1 is based on a VIA ENVY 1724HT chip. No it is not glitchy at all. The problem with it is there is no hardware mixing, so I had to add lines to ~/.asoundrc to mix the the audio. Also I had to edit a line in the mozilla-launcher script to include aoss to make it play sound for flash files.