Powerbooks have only offered stereo sound output on their minijacks: 2.0, not 2.1 (the .1 being a subwoofer output). Some Powerbooks had a third speaker internally, but that was a midrange speaker, not a woofer.
Optical out is offered on the 15 and 17" Powerbooks as a special 1/8" jack that combines stereo out for conventional cables and optical out for a specially made cable (and I thought the 1.5 and 1.67 GHz earlier models, but friggin' Apple still has their hardware specs crosslinked to thre wrong page)
In order to use the Optical multichannel out, you have to have a receiver or a powered speaker set with both an optical input and a Dolby or DTS multichannel decoder. Plus your source material has to be encoded with multichannel sound natch.