Alstein - so far everyone has been giving you tips on a fairly advanced way of transmitting audio to the receiver. Perhaps that's because you have that rare combination of Blu-ray player that has analog outs and a receiver that can actually accept them.
However there is a much simpler option available that you might consider. You could just use a single optical cable or a single RCA/coaxial cable going from the player's digital output to one of the digital inputs on the receiver.
The AVR 135 will transmit a reasonable audio mode such as DTS that even that old receiver can decode, and you'll experience pretty decent 5.1-7.1 sound.
Not everyone has the extremes (of audio gear, speakers, room, source material, the personal listening expectations) that it would make much difference.
If you aren't of the type that obsesses over the nuances of each audio format, then the single cable solution should do fine.
What happening is the that 0's and 1's of your digital audio format (Master Audio, etc) get converted to analog signals eventually, since analog is what comes out your speakers.
Now your receiver can do that decoding, although not some of the newest codecs. So the concept of the 8 wires is to alleviate your audio receiver from having to convert the audio data stream. Your blu-ray player does the decoding, then transmits analog signals for each speaker back to the receiver so they can be amplified directly.
I'm a sound quality nut, but I'll concede that any difference in the sound quality of the two methods wouldn't be noticeable to 98% of the population.