NW-S638FK

The NW-S638FK added speaker support to the 8 GB sixth-generation S Series model. It retained the full unified design and Omakase Channel capabilities. The player features 8 GB storage supporting MP3, WMA, AAC, and WAV files along with the 240x320 LCD, FM radio with recording, speaker output, video and photo playback, Clear Audio Technology, and 40-hour lithium-ion battery life.

This model is a side branch of a stable platform. Sony is not trying to redefine the S line here; it was simply extending an already successful form that no longer needed overexplaining.