Are you sure!!?
Let me guess; Are you losing the right channel when you use your mixing cable?
If so it may be a hardware problem and not your cable.
I've noticed with Model 2 SCD that the stereo jack is of poor quality. Like some cheap headphone sets, they sometimes eventually lose the right channel.
Before purchasing a new cable I would test the suspected bad cable on something else. I test it by hooking my portable MP3 player into the soundcard of my computer, I then use an MP3 that test both the left and right channel.
*Be sure to disable 3d sound effects on your soundcard.
If you are comfortable with a solder iron you can easily fix this yourself. I have soldered a stereo wire onto the SCD board, this then plugs into the Genesis. You could also hide the wire altogether by running the wire through the inside of the SCD and Genesis, then wiring it to the inards of the Genesis.
This has benefits; no visible wire, open stereo jack for headphones, and it also doesn't disable the RF sound if you happen to use this. Normally, when you plug the jack into the SCD it disables the RF sound on the TV.
*Be sure to get the left/right channels right!
Reply if you need tips, I rarely read email.