Connect CD ROM to TurboExpress

[Sadler]

Hi PcEngineFX! I haven't posted here before, but I was reading the 101 PC Engine Secrets page and my curiosity has been piqued. Secret 6 explains that 1 pin is missing to hook up a CD ROM to the TurboExpress. What pin is missing? I'm no EE, but I'm guessing the same chips are present in the TurboExpress as the TG16. How hard would it be to mod a TurboExpress to hook up to a CD attachment? Thanks!