I installed the Lyric in my 1946 Martin 00021 and I am struggling to get a good sound. It works very well for direct reCording but as a pickup for live sound I still have to fiddle with it.
It is apparent that it works very well as an internal mic but it also amplifies every resonance that is inherent of the guitar.
My Martin has a resonance at around 2,5khz that I am not able to dial out with the amps I have. I have noticed this also with my UST and mic combo, but somehow it was not as evident as it is now wih the Lyric.

I changed the position of the Lyric a couple of times:
- under the sadle (on my Martin there is almost no room there for the Lyric as the bridgeplate is there
very close to the bracing and the lyric is fysically stuck between bracings and endpin) : very clear sound but with extreme resonance peaks at around 2,5khz.
- behind the end pins on the bridge plate: same sound but less clear, as if the resonance is now dominating.
- on the top, off the bridgeplate towards the endpin: best result for now, in a way more balanced. Still some correction needed for which I will need a parametric eq probably.

As the direct recorded sound is good, it seems like the sound the Lyric picks up coming back from the amp is an important factor. Logical as this is what also happens when you have a mic in front and run that through a monitor.

Still some stuff to try. I am open to suggestions if another location of the Lyric in this guitar would be an option.