You ask a great question… because your components are known to be very detailed and analytical. I would recommend going to the root of the issue. I would swap out your preamp for a musical / natural sounding one… I recommend an Audio Research (both detailed and natural sounding)or Conrad Johnson (more musical)… or VAC. These are musical and natural sounding first and detailed oriented second.
Then I would swap out the amp for a musical / natural one. Pass XA series, or Audio Research (my preference… see my profile), or CJ.
The issue is that a number of companies focus on details at all costs. It sounds like you have realized the issue with that… sterile sound. The way around this is to get components that are designed to communicate natural sounding music. You can fiddle all you want with tubes and not get around the design parameters.