But his amplifier is already a warm, sweet KT66 / EL-84 based push pull amplifier. So if it's still a bit harsh or etched, perhaps a tube preamp is in order.
As for the 55II being accurate and neutral, just because it's metallic and fatiguing does not mean it is more or less accurate than gear which is warm or euphonic. More likely it's on the lean and fatiguing side of neutral -- steely and metallic is also a kind of coloration.
The best gear that I've heard has great tone, sweet and extended highs, full of body and density, great low end responses, transparent and neutral, and utterly non-fatiguing. But to get all of these things in the same gear, this costs dearly.
For what it's worth, if you only have need of one input, your source has less than 1000 ohm output impedance and your amplifier has 50K ohm or more input impedance, then an LDR based preamp like the Lightspeed Attenuator or the Warpspeed would offer tremendous value for dollar. I have found these types of preamps incredibly transparent without a hint of fatigue (feel free to essage me privately if you're interested in the Warpspeed).