A visual feast is something that is "pleasing to the eye" - very nice, even impressive, to look at. I guess you've already looked up "sumptuous" in a dictionary. The phrase takes the idea of a real feast of food, and applies it to something we can look at. However, this article says that the show focuses more on the music and the musicians instead of creating a "spectacle". Have you ever watched "Later... With Jools Holland"? It's quite good.

Bye, it is still not easy to give a certain explanation, even with all of the data you provide. The performing seal remark helps. Musicians have common difficulties with the clubs they play in. Musicians want total freedom to play anything they want. Those who manage and own clubs want to dictate what the musician does play, and does not play. They often dislike giving full creativity to the musicians. The "sumptuous visual feast" phrase generally means that something is nice to look at. It may be colorful costumes, or half nude bodies, an extravagant setting like a Hawaiian Island with flowers everywhere. Those would be representative of a "sumptuous visual feast". Maybe the musicians are refer to their own uncommonl appearance. Perhaps they are suggesting that as a band, they are not very special to look at? Perhaps they dress shabbily? .