I need help describing the sound of a SET to a friend in English.

How can "the sound of a SET" be best described sans system context and the execution/implementation/design of the SET components within that system?

Let your friend listen to a system with SET amplification and come to his/her own conclusions in comparison with his/her prior references.

A real experience versus a cognitive exercise.

@dekay  Listening to 'K' by Kepa Junkera Urraza right now. Thanks for the recommendation. I spent a few months in Basque country. It's bringing back memories!

- not only the enhanced sense that the performer(s) are there right in front of you, but also a sense of the space around them.

- getting the timbre and the harmonics especially right, making more a richness to the sound.

All of the above is not "unique" to SET amps.

And this is coming from someone who has embraced tubes as well as SETs.