I can't help you with your electronics diffculty but regarding possible replacements- I don't care for the "quack" you get from those under saddle Piezo pickups, some do. I installed a
K&K Pure Mini in my 000-18 Martin and get a pretty decent acoustic sound but better yet is the L.R. Baggs Lyric that came installed in my Slope D. I do like the convenience of a low profile
volume control in the sound hole and you can move it up slightly so it's not visible. I'd listen to various pickups, as best you can, and if you have any doubts about your ability to do a proper installation by all means take it to a competent luthier.