As I understand it, the only way to get surround sound out of a MacBook (or pretty much any Mac) is either (1) a digital set of 5.1 speakers using an optical cable, or (2) an external sound card.
Actually, you can get 5 channel matrix surround out of a R/L "analog" audio signal. This is how Dolby Pro Logic (R, L, C, rear mono) and Dolby Pro Logic II (R, L, C, RR, LR) is done. It's actually quite good, but doesn't provide the channel separation or LFE like digital audio does (e.g., Dolby Digital or DTS).
Also, thegoldenmackid speaks the truth - music isn't going to play at 5.1 unless it's a DVD Audio disc.
There are a few CDs recorded in Q-sound, which can give you >2 channels of audio, but it hasn't taken off and I'm unaware of any receivers/amps that can decode it. I remember listening to Pink Floyd's Dark Side of the Moon on a quadraphonic system (turntable) back in the 1970s. Unbelievable sound, yet you really can't get it today without DAD and the player to go with it. It is strange why they don't record in Dolby Digital, DTS or even DPL. Seems like a perfect marriage for audiophiles.