WIth further research it seems that there is a standard for the LFE channel and it's up to 120Hz.
I've also been having a look into my receivers settings and options and it seems that it is processing the signal from the multi channel inputs before passing them through to the pre-outs. It's certainly applying volume controls to each channel and it could be applying EQ as well (although that might be to the overall signal). If it's converting the analogue signal back to digital and then back to analogue again then I'm wasting my time converting it with a decent sound card.
Basically, I need to understand exactly what processing is going on with my signals before I can begin to EQ them. I really appreciate the help and advice I've received so far and, if it's ok, I'll take that away, work out exactly what's happening and then come back with a fresh set of graphs and a knowledge of what I can and can't control.
Two good things have come out of this already so far though: it seems that I have more control over my crossover than I though previously and I have a hugely extended bass response from moving my subs about.
Thanks again guys!
