I checked A6 setting, If i remember well Dave ports are write only, reading them results alway 0ffh, therefore A6 setting of the game is always 0ffh, which sounds the same for my ears as 10h. Other the sounds are good I think, I played with one sound, when all two players owns the puck, and the sound was much better when I decreased the volume from 3f,3f,2f,2f to 1f,1f,0f,0f, so possibly it is enough to play with the volumes to get the best sounding.
Reading A6 I think can be removed, except if you use other A6 setting elsewhere, I would suggest to load directly A6
01E6 3E 10 LD A, 10
01E8 D3 A6 OUT (A6), A
instead of
*01E4 DB A6 IN A, (A6)
01E6 F6 10 OR A, 10
01E8 D3 A6 OUT (A6), A
other, the code could be smaller and littlebit faster:
at 03c3h setting the volume
OUTI
SET 2,C
OUTI
instead of
LD A, (HL)
OUT (C), A
INC C
INC C
INC C
INC C
INC HL
LD A, (HL)
OUT (C), A
at 03d4h resetting the volume:
XOR A
OUT (C), A
SET 2,C
OUT (C), A
instead of
03D4 AF XOR A
03D5 ED 79 OUT (C), A
03D7 0C INC C
03D8 0C INC C
03D9 0C INC C
03DA 0C INC C
03DB ED 79 OUT (C), A
at 03edh reset all volume registers:
XOR a
OUT (0A8h),A
OUT (0A9h),A
OUT (0AAh),A
OUT (0ABh),A
OUT (0ACh),A
OUT (0ADh),A
OUT (0AEh),A
OUT (0AFh),A
RET
instead of
03ED XOR A
03EE 0E A8 LD C, A8
03F0 ED 79 OUT (C), A
03F2 0C INC C
03F3 ED 79 OUT (C), A
03F5 0C INC C
03F6 ED 79 OUT (C), A
03F8 0C INC C
03F9 ED 79 OUT (C), A
03FB 0C INC C
03FC ED 79 OUT (C), A
03FE 0C INC C
03FF ED 79 OUT (C), A
0401 0C INC C
0402 ED 79 OUT (C), A
0404 0C INC C
0405 ED 79 OUT (C), A
0407 C9 RET
