Hmm … have to compare those files again. But I am pretty sure, if i modify my original WACO instruments.xml (about 4K) by adding the two sections from the PA44 instruments.xml, you mentioned as missing (CARENADO_INSTRUMENT_HSI_Tape_Template and CARENADO_INSTRUMENT_HSI_Gyro_Template) the result is still way shorter than the file you provided on your google drive, while indeed fixing the non working HSI in the PA44.
Sorry for being confusing 