I'd say what I heard as being 'sucked out, was high end. If you got a nice jazz with new steels, put it through your amp and get the tone so its real bright, without having the wah in your chain. The slap and pop for a bit. then put it in the chain, and see if you get exactly the same tone.
i did it a little differently, but I used my Korg PX3B and ran it into my computer to make the comparison. Its not huge but it was there.
But, then again, I have been known to be on crack. So any of you owners, do this. Take the battery out, and then plug it up. If you get the same sound, good stuff and I am wrong. Otherwise, there is active circuitry it is going through. and that will have, if nothing else but infitessimal, a difference.