I'm ready for my next tuning.
This time I got the Korg CM-300 and the signal is coming through very nicely isolated.
Unfortunately, pianoscope seems to have difficulty detecting notes, often in the high treble or low bass.
I used to think this was due to low volume or something, but now I'm not so sure. It could be the algorithm is rejecting the signal as a piano sound? Often, manually selecting the notes helps but not always.
It's really strange, because pianoscope will detect a note that's a little higher but then not detect the lower note. Or vice-versa. Perhaps there needs to be a setting more optimized for contact mic -- a lot of the processing to exclude external sounds shouldn't be needed.