Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
Q:1/4=110
M:2/2
K:Dmix
['B AD GF/E/ A,D (G/F/E/D/) GA B/A/G/F/', 'Ad fe/d/ ad fe/d/']  
X:1
L:1/8
Q:1/4=110
M:2/2
K:Dmix
|:"^A" B | AD GF/E/ A,D (G/F/E/D/) | GA B/A/G/F/ BEEB | AD G/F/E/D/ A,DFA | Bd A/B/A/G/ FD D :: 
"^B" d | Ad fe/d/ ad fe/d/ | gb/g/ fa/f/ beef | Ad fe/d/ ad fe/d/ | Bd A/B/A/G/"_(1)" FDDd | 
 Ad fe/d/ ad fe/d/ | gb/g/ fa/f/ beef | df/"_(2)"d/ Bd/B/ A F3 | GB A/B/A/G/ FD D :|  