I have owned both the HTS and now the S1000. The preamp button, as the manual describes bypasses the digital processing circuitry. The idea is that the digital processing somehow degrades an analog signal, such as a phono.
I never could tell much difference with it. What I could tell a difference with is the S1000 versus the HTS. The S1000 has a much better sound. Whether listening to music or movies, the difference is noticeable. I have mine hooked up to various Krell amps, so I can't comment on the S1500.
I never could tell much difference with it. What I could tell a difference with is the S1000 versus the HTS. The S1000 has a much better sound. Whether listening to music or movies, the difference is noticeable. I have mine hooked up to various Krell amps, so I can't comment on the S1500.