[blue_max]

Here's what I have learnt...

Firstly - remember this principle. You have now got the maximum signal from the LFE port of your amp into the bfd. The only things that will affect this now are the amps volume (which you have decided is as high as it's ever likely to go) and the actual volume on the sub's amp itself. The sub could be on zero volume or max and the bfd won't care. You need to balance the subs volume to match the other speakers.

The amp should have a test tone and either manually or automatically sweep to each speaker. This has a set volume of 75db (I think this is universal to all amps). Sit at your usual position and ideally use a tripod to mount the meter vertically (microphone at the top). Set it to the 70 range, c-weighted and slow. When the sound plays, you need to adjust the speaker volume via the amps channel adjustment. The needle needs to sweep past the middle and settle at +5 to reach 75db. When it comes to the sub, you need to adjust the sub's amp volume - it is not easy to measure, but see if you can it's sweep at the middle of +5. You then have your speakers balanced.

When you use REW, it's best to use the 80 scale as it gives more headroom.

Hope that helps.
Graham