Bottom line is, you won't get surround sound to pipe back through the HDTV to your older Pioneer receiver. It may be possible for you to achieve matrixed (not true) surround sound though, if you split your connections somehow.
I have experimented with HDMI from Blu Ray player to HDTV, then digital optical to receiver. If you provide the exact model number of the Blu Ray player, I can take quick peek at the manual online to see if this particular audio configuration is possible. Some brands/models permit this, like you can on an Xbox (etc.). It can get you DD5.1 and/or DTS, but won't give you Dolby HD and other newer audio soundtracks.
Any digital optical from HDTV back to receiver should always be used as a last resort, basically.