Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
Q:1/8=100
M:6/8
K:Amix
['A A F', 'D D', 'z A', 'D D']  
X:1
L:1/8
Q:1/8=100
M:6/8
K:Amix
 A A F A A F | G G G F E z |: D D D D G E | F D D D A, z :| A A A F d z | A F G F E z |: 
 D D D D (GE) | _F D D D A, z :|  