No, your receiver will not accept multichannel analog. This is considered a "premium feature" now on receivers, and is generally considered to be an outdated feature on low-end receivers.
Besides... optical and HDMI will give you better sound unless you have a high-end analog sound card feeding the receiver.
I guess it must not really be that important.
It would have made things easy, though, since I'm already running analog from the computer to where the receiver will be.
Be aware, optical will only do regular DTS and AC3. You will not get Dolby-HD or DTS-HD unless you have an HDMI output that will stream this to your receiver. Unfortunately, your 4000 series Radeon will only do LPCM... which is just as good as Dolby-HD or DTS-HD... but the fancy Dolby/DTS-HD light you paid for on the receiver will not light up.
Well, I didn't buy the receiver for those two options, so I guess it doesn't matter.
If optical will only do DTS and AC3, will HDMI do AAC?
I did notice that AC3Filter might convert AAC to AC3 in real-time, although I'd have to figure out how to make XBMC use AC3Filter instead of its default (FFDSHOW?).
You could go two routes... optical will be the easiest to get setup, and will get you excellent sound. HDMI with your current video card will get you excellent sound but may require you to fiddle a bit to get it to bitstream multichannel LPCM. Plus technically, you will be running two video outputs (HDMI to the receiver going no-where, and the VGA to the projector)... but that shouldn't be an issue with your beefy card... just be aware that you are running two displays. You'll want to make the projector the primary display.
I guess it's not that big of a deal to have a non-used secondary display.
It just seemed kind of pointless (I'd have to make sure no programs accidentally opened there).
Oh, and why do you need a 30' optical cable? Is your HTPC really that far away from the receiver? Check monoprice.com for good prices.
It's not that far in a straight line, but 27'-28' is pretty accurate.
I have the computer sitting next to the couch on the open side of the room.
I could move it to the other side of the couch, but then it would be sandwiched between the wall and couch and next to a register (not good for heat).
I might be able to put the computer in the front, but then I'd have to deal with vga cable length to the projector.
I do have a lengthy vga cable, but it may not be that lengthy (I'll have to check, tomorrow).
If that works, then I wouldn't have to buy such a long cable for the audio part.