The S-300 needs to be left powered on all the time to achieve optimal performance from it. Still even under those conditions that thin somewhat edgy sound is typical from the the generation of ICE modules used in that amp as they are from quite a while ago. I owned a pair of W4S mAmps with modules from the same generation and they sounded similar to what you describe. Never heard Dusty's Channel Island amps but I do own a Nuprime ST-10 and it sounds nothing like the S-300. Much more refined amp in every way. For a SS preamp that meets your stated requirements look at the Van Alstine Vision SLR.
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