A schematic really won't be of benefit here.
I can give you some guidance on connections, but the amplifier is the real limitation here. This is a very old and very basic model stereo only amplifier. It will not give you surround sound, just basic stereo sound through 2 speakers.
It is also an entirely analog device, so it isn't directly compatible with your bluray player or most of your other devices.
Your best option here would really be to replace the technics entirely with a proper surround sound a/v receiver.
If you aren't able/willing to do that though, you can use it to get limited stereo sound. What you'd need to do is to connect all of your source devices (bluray, dtv, xbox) directly to the tv via hdmi. Then you'll need to buy a digital to analog converter box: http://amzn.to/1QLbaBd
Connect that to the tv's Digital Audio Out port with the optical cable, then a set of red/white out of the converter to any input (cd, aux, etc), and set the amp to that input.