Hi Baldrick - cheers, yes, you're right - but I prefer the directional rather than diffuse surrounds (have tried both). Probably loads of people reading this are pursing up their mouths in disgust. Anyway, it would seem that if the rears are pointing towards me at head height, most of the sound will end up hitting the back of the sofa which ain't good.
I suppose I'll just have to try a few things out. Chuck the Nazgul attack on Osgiliath in ROTK on a permanent loop!