It sounds good to me. Same tip as i got in this
thread, though: At least one channel (probably square) should see conservative use, lest essential parts will cut out when sound effects take priority. Since this music is intended for boss battles and levels; it is something to concider. Be extra wary of anything other than echoes, short, supporting blip/percussion notes and possibly secondary harmonics.
afaik, there's no currently available VRC6 pcb for homebrew cart production, if that's your aim. Running on emulator; no problem. Physical copies? More so. (The one that's available is the Sunsoft a/b, and even so, the sound chip option lends a quite expensive and impractical price per unit; adding ~$10 on its own).