Another update to the source code here:
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

This implements the proper responses to the head unit's queries for track metadata, in cases where it attempts to query for multiple pieces of metadata in the same query line.

I haven't gotten a chance to see if this fixes the problem with my roommate's Kenwood stereo yet. Crossing my fingers!