Voodoo: I would pull the second set of speaker cables off of the speakers and take measurements with a single cable and jumpers hooked up. You can then hook things back up and take another set of readings with the complete bi-wire arrangement. I sincerely doubt that you'll see any major differences.
Other than that, it sounds like you might be running into some form of cancellation from room nodes. The spacing between 800 Hz and 2600 Hz almost equals a primary and a third harmonic, so that could be coming into play. Then again, you might have a node at 800 Hz and the 2600 Hz drop could be crossover related. Too many variables without knowing any of the specifics.
As to the RS meter, none of them are real accurate in stock form. I know nothing about the digital meter, as i've never used it or read about it, but you can probably find out how to correct a lot of the deficiencies of this unit at
Eric Wallin's DIY Audio Website. Sean
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