As a fingerpicker who wants to avoid batteries in my guitar, I've generally used the Baggs LB6 to much satisfaction. However, I have an old Guild that is my "strummer" guitar and I didn't think the LB6 would be a good fit for that when performing. I wanted a soundboard transducer that was passive, not boxy sounding, and would work with my Baggs preamps. It's hard to find the iBeam passive but Shoreline has it and I ordered one. It installed easily with no glue (!) and no other modification besides the endpin jack. I had been warned that it's a quiet pickup but I didn't find that it needed all that much gain to produce a good volume. Run into my Fishman Loudbox Mini with the volume between 1 and 2 o'clock, I only had to set the gain between 12 and 1 to get it up to power (for strumming, fingerpicking might benefit from more gain). There was no excess bass, no harshness in the high-end, and best of all, no feedback.
I haven't had a chance to gig with it yet, but I imagine that it will only benefit further from the detailed EQ and notch filter available on my Baggs Para DI. Perhaps it's just a good match for this particular guitar but I would sincerely recommend anyone considering a K&K to give the passive iBeam a try. I think it has an exceptionally natural tone for a SBT and doesn't seem to suffer from some of the issues common with soundboard transducers.