Then I don't understand how adding the Amsdos header is useful. Not that I'm against the idea, but I don't understand the purpose.
The Amsdos header will only be added to the music itself, not the player. So you will have to add it to the player anyway, with another tool. Why don't you use this tool with the music too?
I have no idea why your prod doesn't "like" the AT2 player, but I assure you it is supposed to work fine

.
My advice is: download Rasm, use it to compile the music and the player at specific location (for example, player in #3000, music in #4000), as a test. Load the binaries at these locations. Then, in your code, make a:
ld hl,#4000
xor a
call #3000 + 0 ;Initializes the song, subsong 0.
Then make a loop, synchronized with the video sync and at each frame:
call #3000 + 3 ;Plays one frame of the song.
This WILL work (makes sure your code doesn't overlap over the player and the music). If not, maybe you should ask for help on the CPCTelera forum, because the problem must be specific to it.
That's only the beginning. When it works, put the music and players at more handy location and then you can forget about it!