AD-7173A & AD-7173s firmwares

Considering that Sony AW-G173A (Optiarc AD-7173A) and Serial-ATA version of this drive share the same hardware, is it possible to flash AD-7173A with a AD-7173S firmware?

i think the answer is no, since the drives use different techniques to transmit the data from and to the motherboard, but maybe someone with more knowledge can correct me.

I think you misread something. AW-G173S and AD-7173S share the same hardware, just like AW-G173A and AD-7173A. But the A and S versions are likely to be different.