The variety & multitude of suggested corrections & mods seems fairly overwhelming; who knows it could be any, or a combination, of the above.
One area I haven't seen addressed nor do you mention, is what AC cables you're using. Since the CDP is satisfactory, you might experiment with upgrade AC cord on the phonostage alone. Or line conditioning. Perhaps even footers or an isolation shelf. All of these can change sonic signature to a lesser/greater extent, especially with tube componentry.
Some here would argue that cabling & cords can't possibly affect the sound of a component. However my own tuning experiences with changing AC cords (and to a lesser extent, line conditioning) have proven that a world of difference can certainly be realized.
Just another mystery to throw into the mix - sorry ;-)
One area I haven't seen addressed nor do you mention, is what AC cables you're using. Since the CDP is satisfactory, you might experiment with upgrade AC cord on the phonostage alone. Or line conditioning. Perhaps even footers or an isolation shelf. All of these can change sonic signature to a lesser/greater extent, especially with tube componentry.
Some here would argue that cabling & cords can't possibly affect the sound of a component. However my own tuning experiences with changing AC cords (and to a lesser extent, line conditioning) have proven that a world of difference can certainly be realized.
Just another mystery to throw into the mix - sorry ;-)