It’s not 8 bits. Most of the Yamaha chips seem to use 16 bits internally in 8.8 format (based on Raph Leviens work). Different models of Yamaha chips had differ

It’s not 8 bits. Most of the Yamaha chips seem to use 16 bits internally in 8.8 format (based on Raph Leviens work). Different models of Yamaha chips had different DAC setups, but on the DX7 the representation was 12.3 floating point - which I think was converted from the internal log scale fixed point to linear scale via a lookup table. So while the DX7 chips technically use both floating and fixed point it probably does all arithmetic in fixed point.