As you are aware the WAHT-SBP2 kit provides a way to wirelessly add a pair of surround back speakers to the BDV-E370, thus giving you a full 7.1 surround sound system. The WAHT-SBP2 kit is very difficult to find - likely because it has been out of production for a while. Sony has produced several other S-AIR transmitter and receiver/amplifier products that are compatible with the BDV-E370 but my understanding (anyone please correct me if I'm wrong about this) is that Sony is no longer producing any S-AIR products.
There is no other way to add surround back speakers to the BDV-E370 other than with use of Sony's S-AIR based wireless speaker systems, because the BDV-E370 provides neither preamp nor speaker outputs for a pair of surround back speakers.
IMHO - not being able to set up a 7.1 system with the BDV-E370 is no great loss since there are relatively few Blu-ray movies that provide 7.1 discrete channels of sound. Many people are of the opinion that the "sound experience" obtained from a pair of surround back speakers is not worth the extra cost (and intrusiveness) - and that you would be better off saving your money for an eventual upgrade of your entire sound system to a standalone AV receiver and better quality speakers.
