I use for ROM 2 tools GPT and Libre office calc
For example i try made sound track of zelda ( Overworld 1986) , so GPT create me a list of hex for note . I have midi and I was crate a data in libre and coppy and pasting for 3 ROMS(16 s per one ROM) this method is suffice me
I saw your last pixel art and You used decoder 8 to 255 and you used logic ,for this , why ? You can use rom first 00-FF make column second 00-FF row and one 3 state buffer per enable ^^
I hope that it was helpful