This is not very High End Audio of me, but let me offer another solution that is cheap and fun: The Joilda (Fosgate-designed) Foz SSX. I bought one for use with headphones when I had a job that would take me away from home for two months every year.
It can go between your preamp and power amp. It does three things: it is a tube buffer, and changing its single 12au7 tube has great and fun effects on sound. It has a bass control that I think of as a thickening agent, as it increases the bass, and also thickens the lower midrange just a little. And it has a crossfeed circuit (that's the Sound Stage Expander, or SSX portion) that lets you play with the width of your soundstage.
Again, I used it for headphones so I could have some control over the soundstage of my phones, while adding or subtracting bass. And to warm up my good, but somewhat cool headphone amp.
Recently, I have tried it with an inexpensive solid state amp, and I can't get over how much it improved the musical enjoyment, and at a relatively low cost to fidelity. Might be fun for folks to try. We can't be purists all of the time...