In a few days I expect to install the Lyric in my Martin OMC-1E. Wanted to get your inputs/opinions on my installation plan ...

This guitar has its original undersaddle pickup and side-mounted preamp. I totally dislike the sound of undersaddle pickups, but plan to retain the pickup and preamp in the guitar just so I may use the tuner function on the preamp. I plan to keep the undersaddle pickup in place and connected to the existing preamp, but will disconnect the preamp from the endpin jack (I will just be using the endpin jack that comes wired with the Lyric; and having endpin jack disconnected from existing preamp also ensures that it remains turned off). Now since the existing preamp provides convenient barn-door access to a 9V battery, I am considering having this be the only battery in the guitar. I can connect this battery to power the Lyric's preamp in parallel with the existing preamp. I figure that the existing preamp should only draw current whenever I turn on its tuner function and should not draw current at other times; So I believe this should not diminish battery life or limit the availability of current to the Lyric, except during those brief times when I turn on the tuner.

Do you think I may be overlooking any critical factors in my plan? Have any of you gone this route before? Am I better off simply having the Lyric connected to its own battery? Looking forward to your inputs ...