If you were using the analog output on your Powerbook I would say that you could get better sound out of a dedicated player. Seeing how you are outputting a completely digital stream, the sound you hear is only affected by the DAC. You should also not have an issue with packet loss. Wireless systems are very good.
So, to be brief, no. If you are unsatisfied with the sound, look into your room's acoustics, the flatness of your freqency response (affected by acoustics), and finally, think about a different DAC. The DAC should be last, as it will affect your sound much less than the speakers (I assume you like your B&Ws) and the acoustics. An all-out purchase would be a Benchmark DAC, but it is also an expensive piece (~$900). You would be better off purchasing a device like the Behringer DCX2496 to help smooth out your frequency response.