Mod aux input old cd player?[LA4227 Sanyo]

[ByoXFPD]

Hello, Ive been working on adding aux inputs to some old cd players, so far i got the required info and i understand a good portion of it:

Datasheet:

LA4227 datasheet(3/4 Pages) SANYO | Audio Output for Radio Cassette Recorders 3W × 2ch Power Amplifier

The In1 and In2 are obviously L/R channels but i got a bit lost on the GND one, should i use the PREGND or im missing something?

I've read that the audio GND is the same as any ground, but i highly doubt its the same as the device GND or VCC GND

 

[thiagoas]

The application circuit shows all GND tied together.