Well red roses and melodies are also objects, just different kinds of objects. To be compared to a fine musical instrument might even be seen as quite a graceful compliment.

Less graceful perhaps, but also compllimentary is the old saying "There's many a good tune played on an old fiddle," which reflects the sexual imagery of such instruments, which they share with the similarly waisted guitar.

But as for the question can we date the instrument imagery to before 1794, the answer at this point is, no, and not till a long time after. So the question is, when did it originate and get linked with the red red rose?