Taken from the intransitive verb:
To “wax” is normally seen in the sense of increasing, as the moon waxes and wanes in its cycle.
However, to wax also means to become, to tend towards, to grow towards. One can wax indignant, or wax lyrical, or wax rapturous, meaning you become/tend to that state. The word is old, tracing back from the high German to the Greek.
Wax is appropriate in the music industry as Edison first tried recording sound on a wax-impregnated paper tape when he invented the phonograph, later developing into the “record player”.