If the internal spu works and the others don't i think it has to do with some spu irq problem. Have you spu irq hack enabled under sound->config? If so, you probably can make the game work using peops or eternal, but you'll have to tweak their internal spu irq fixes to make it work. You should try, eternal and peops sound way better than the internal one.
BTW, about the graphics, with that card you might consider using peops gpu plugin. Will look worse, but gives more chances to get the game working as it's expected to do.
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