Pickup & Preamp Recommendations for Archtop Bass

I am looking to the replace the Ghost piezo monorails and preamp on my Washburn AB40 Stu Hamm model. They sound okay, but it's a noisy system with low output. I was thinking that Ibanez monorails & preamp might work. The bass is semi-hollow, so my first choice (K&K Pure Sound) won't work -- the block under the bridge is in the way. I hate to toss in the towel on this instrument, so I'd welcome your suggestions. I'll have to find someone to do the work, as this is not my line. Thanks for any help you might be able to offer.
 
I am not sure it's working correctly, but my luthier was unable to improve the situation, so I'm at a loss. The original owner had nothing good to say about the electronics and stuck a Basslines mag pup into the soundhole. I prefer piezo for this bass, and it does sound good. It just hisses like mad when I turn up the treble, and I have to crank my amp to get a decent amount of volume out of it.