I enjoyed your piece! You have good contrasts in characters that matches their differences in opinions. I can almost hear the guitar strings as the music is played. I do think there are a few things you could do to improve the flow.
The first sentence captures my attention, but is confusing. You say 'as he plugged it into' but only Stuart is mentioned so far, and he is across the room. I believe abashed is a verb or noun, not an adjective, so it can't describe a smile.
The speaker belched to life as it was plugged into the outlet. Across the room in his recliner, Stuart twitched at the sudden noise. The old man offered an embarrassed smile and said, “Sorry,” in a voice trembling with anxiety.
The second paragraph is also important since, I believe, you are telling more about the musician than his appearance. I thought it might be good to connect the information about the musician's eyes to give clearer hints.
His face was ageless, with smooth features. A tribal tattoo wound from the left side of his jaw and plunged beneath his collar. His meaningful stare reflected a depth of centuries through silver eyes. He grinned, “Jitters happen sometimes.”
Later you say, Stuart’s face trembled, becoming motley of emotions. I believe it should be 'motley with emotions'.
I hope you find this helpful, and, of course, these are only suggestions. I think your beginning needs to be clearer, whichever way you think is best, so the reader continues into the interesting story you present. It's a good one! Good job.