Buckle up, this post is as much to organize my own thoughts as it is to inform others...
The tale starts in 2010 when I did a basic stereo system upgrade a bought a cheap but effective YAMAHA RX-V365 receiver. Some time later I found out that particular model had an annoying limitation of not being able to separate out the audio from an HDMI audio/video stream so inputs from my devices couldn't just use one cable. Not a huge deal, my HTPC has always had optical out so HDMI plugs directly into the TV and optical into the receiver.
...but then I had to go an get a Wii U - which doesn't have the ability to output audio over anything but HDMI if you want a digital video signal. Now I was stuck using my TV's speakers for the new console, not ideal. Without thinking too much about it I bought a 1x2 Pigtail HDMI Splitter from Monoprice thinking I could just stick one cable into the TV for the video and the other into the receiver to get audio - no such luck (I should have known better based on the limitation I already knew my receiver had). So last week I decided to look again for an HDMI/optical splitter and unlike when I tried looking for the same thing last month I found an affordable one on Amazon made by ViewHD. It arrived yesterday and while it does allow me to finally connect my Wii U to my receiver for vastly improved sound I can only get stereo from it as it turns out the Wii U only supports 5.1 via uncompressed LPCM which optical audio cables can't carry (and my receiver couldn't handle anyway).
So it turns out I'm in the market for a new receiver as there is no other way to get 5.1 from the Wii U. It's kind of lame that Nintendo didn't pony up for Dolby Digital licensing or something but I guess its ok considering they at least went for the highest quality output available. I guess I should have done more homework first or the ~$70 I've spent so far could have been put toward a new receiver instead... Of course I did find this guy that would apparently take the LPCM 5.1 signal from the Wii U and give it to me as analog outputs but I really don't like that option.
That's where I am today - about to start the process of picking a new receiver - will update this thread with my choices and with how things work out.
Edit: Ugh, what a rabbit hole Wii U surround sound is (read the NeoGAF thread linked above)... I think I'm going to pick the YAMAHA RX-V373 as my new receiver though, in addition to solving my Wii U surround sound issue once and for all it will simplify my AV cabling a bit.