Porting is harder than programming, since things that work perfectly on one system, may not work at all or may produce bad results on the other system...
For instance, on the subject of game porting, Hideo Kojima made the comment that it was so difficult to port Metal Gear Solid 2 from PS2 to Xbox, that he would never port another game as long as he was in charge.
The reasons were that filters used in almost every scene for general basic effects looked completely different when similar programming was executed on the Xbox hardware, thus taking months to rework a fundamental process of the game. Other things involving collision and event code were also factors.
The same is true of PSX > PC porting. The hardware a PSX uses does not compile the same type of scripts with the same processor or language or in a few cases even the same byte cluster size...
Not only that but FFIX specifically has a menu system that is difficult to emulate, causing massive slowdowns on several drivers... (including the PSX emulator for PSP)
However.. if someone WERE to write a ported FFIX engine I would kill to get my hands on it... since it would likely have the ability to modify, add, subtract, and queue practically any scene or module...