I'm not sure if you will hear a difference with an optical interface between the Blu Ray and receiver.
You reallly need a receiver with HDMI to support the lossless audio soundtracks, there is too much information to send over optical or coax, needs to use HDMI.
The other option is if the Blu Ray has 5.1 or 7.1 outputs, and your receiver has those inputs, then you can let the player do the decoding.
Randy