The Pioneer A400 Amplifier is capable of fantastic sound-quality.
Once upgraded you get a smooth sounding amp, with terrific levels of detail. Bass punch & dynamics are improved dramatically too. The re-worked mains cabling opens the sound up further, resulting a more realistic, cleaner midrange and treble.
The Stage 3 Upgrade builds on the Stage 2 upgrade by adding in an active audio buffer to the signal path. This active buffer "drives" the volume pot, and dramatically reduces the load on your source(s) output stage.