ok ill get one and have a mess if i have time
quite a lot of bits and bobs, but the relevant stuff is:
USB sound card
hdmi switch
2x hdmi cables
3.5mm Y splitter
4 port mini hub.
plan is to go:
Graphics Card - HDMI cable - HDMI switch - HDMI cable - Monitor - 3.5mm cable - Headphones for PC audio
PCI Sound card - 3.5mm cable - 3.5mm Y spitter - Headphones, for PC Mic
PS3 HDMI - HDMI cable - HDMI switch - HDMI cable - Monitor - 3.5mm cable - Headphones for PS3 audio
USB Sound card - 3.5mm cable - 3.5mm Y spitter - Headphones, for PS3 Mic
then it is as simple as a flick of the HDMI switch to change between PC and PS3.
A lot hangs on the USB Sound thingy being compatible, but i don't think i have ever seen anyone say the one they tried isn't, so we shall see.