Line level doesn't require amplification. Line level is just a standard established to represent that the output signal is at the best dynamic range possible. If the DAC is outputting the signal at the best dynamic range over a standardized reference voltage, it is at line level. If you look into the idea behind iMod and diyMod, they basically just reroute the line out directly from the Wolfson DAC to the dock connector or mini jack, bypassing all the amp section altogether.
Fuze's SoC (AS3525) is slightly different as the line-out section of the chip has a small integrated amp section which allows for variable output (meaning the line-out can output lower than line level signal). Actually all three of AS3525 outputs (speaker- headphone- and line-out) have independent amp sections. In early Fuze firmware, you can change the line-out level just like the volume control on headphone-out, and this was criticized (and questioned) by users for not being a true line-out (in conventional sense, line-out should be constant). In response, Sandisk disable the variable control on the last of the latest firmware so line-out only outputs constant line-level signal from that onward. One of the funny thing is, the same SoC has been used on other Sansa players (mostly v2 player) as well but with the variable line-out disable as default and users never question the authenticity of the line-out. By enable the variable feature on Fuze, Sandisk actually gets negative publicity. No one would have complained if it was disable from the beginning
