I have an Onkyo receiver and I would like to know if there is anything out there to split the back speaker's signal in two so that my 6.1 surround sounds like a 7.1.

I would like to have a SBL and a SBR without changing my receiver. I would like the two new back speakers with a stereo sound. I know that if I simply add a new speaker both back speakers will be mono.

Is this possible? Is there a chip that I can instal to do this??

Thanks in advance to those who will reply.