HDMI to TV and optical (toslink) to audio receiver is definitely possible.

Or an optical switch; I have four optical outputs going into a single optical input on my receiver.

Amazon have some listed under optical link splitter.

I used a splitter but reverse it, since I only have 1 optical input on my receiver and I have both PS3 and 360. I have toslink from PS3 and 360 both go into the splitter and then from splitter to receiver. However PS3 and 360 can not be on at the same time (which usually wouldn't be the case most of the time).

I use this switch:

http://www.joytech.net/1/products/av/9/79/AV-Control-Center-245C.htm

But if you're looking purely for an optical switch only, you could check out something like this (of which there are several on Amazon):

http://www.amazon.co.uk/Toslink-Selector-Optical-Devices-Connected/dp/B000LB0VGG/ref=sr_1_9?ie=UTF8&s=electronics&qid=1215466070&sr=8-9