If a amp sounds by itself I would never buy it, it's a amplifier not a effect machine. I own iFi micro iDSD and Chord Mojo both strict neutral output with zero change in sound signature, because good solid state amp products don't sound. I also owned the old FiiO E12, so from the K5 prevoius version, it also was strict neutral output, no change in sound signature, a good amp. If you want change the sound go for i.e tube amps, or amps with high output impedance, this will change sound signature for 'warmer' / 'smoother' sound.
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One good advice would be to put a lot more emphasis on signature, it helps people get an idea of how something sounds before buying it!