The audio chip of the SNES was designed by him and Sony.

The Nintendo S-SMP is the audio CPU of the SNES video game console.

The SNES contains a sound module called APU (Audio Processing Unit) which is almost completely separate from the rest of the system: it is clocked at a nominal 24.576 MHz in both NTSC and PAL systems, and can only communicate with the main board via 4 registers on Bus B. It was designed by Ken Kutaragi and manufactured by Sony, who subsequently entered the video game console industry with its PlayStation brand.

http://en.wikipedia.org/wiki/Nintendo_S-SMP

This was what led to the CD partnership, though Nintendo really needed to have looked at the contract they signed for it. This is also why the GBA's audio wasn't as good as the snes'.

Also Sony used to make games for the snes