What model Sony receiver are you looking at? I don't know what "4 HDMI receiver" means in this context, because it could be 3 inputs and 1 output.
You can't really add an AV receiver to and all-in-one HTiB. An AV receiver, speakers and separate DVD/Blu Ray player are what you buy instead of an HTiB. Your HTiB still has no video inputs and therefore no way to send video to your TV, and very limited ability to accept audio inputs.
An AV receiver will do nothing unless you connect speakers to it. It cannot send digital audio to another device because its function is to receive audio from other sources, amplify it and send it to its own speakers. You may or may not be able to use the speakers from your BDV-T10 on the new receiver If you can, then you should be able to connect the HDMI output on your Sony BDV-T10 to one of the HDMI inputs on an AVR, just as if it were a stand-alone disc player instead of an all-in-one. Oh, wait. No, that won't work, either. The wireless rears won't work with a new recevier.
Basically your best best bet is to sell the Sony and buy an AVR, speakers and a Blu Ray player. Because you've really reached the lmits of what the Sony can do. Wish I had better news, but that's where you are.
Regards,
Joe