I think you would be happy with a Musical Design 100 amp. Musical Design/Musical Concepts builds amps with several levels of upgradablity. All of the resources they put into their products goes into electrical components that actually create the sound. The 'box' is just a rectangular, basic black box.
I have the highest iteration, the MD hybrid Elite, which has a tubed output. The sound is a wonderfully smooth, musical and neutral to my ears. I find that all of your requirements could be met by this amp. The solid state version is 'only' $2000 new.
I have the highest iteration, the MD hybrid Elite, which has a tubed output. The sound is a wonderfully smooth, musical and neutral to my ears. I find that all of your requirements could be met by this amp. The solid state version is 'only' $2000 new.