Any reason why you don't just use the Presonus for everything?
You could consider one of these 1/4" stereo to dual 1/4" stereo connectors - then you'd only need an amp with a single input:
The creative card provides better DSP for gaming like CMSS3d positional surround simulation. As well the mic is use for gaming works better with that card.
About the splitter. I was worried that the outputs from the two cards would then be wired together, just by how the connector works. So when onecard is running, that signal is being sent to the output of the unoperationl card.....which would not be a nice thing to do. Is this correct thinking?