wow i like sampled fm for a change! the layered square wave is a good optimization - only improvements i can suggest is having them be more staccato, especially at the beginning, to better match the original (a small detail, but you can't really slip any sonic music details past me!!!). using the empty channel for the other psg channel in the second half of the song could also work, but its definitely hard to notice and as it is now it deffo sounds fine. good stuff!!!