I'm not sure why you would want to use both at the same time?
Does your TV not have an optical port for passthrough?
No. Not many (in fact I just bought a full hd Sony Bravia 40" and even that doesnt) TV's this side of the Atlantic do.
Markleshark is correct
Besides if the 360 can do it. If even the PS2 can handle sound optical two output sources, I fail to see why Snoy can't implement it in the PS3. It's a pain in the arse having to change the setting in the menu each time.