They put him and the piano in a big makeshift sandbox, didn't they? This is part of Beach Boy history and can't be any more embarassing than certain other occasions over the years.
I saw it the night it was broadcast in 1976. I was just recently hooked by the "Brian's Back" campaign. A very young Jodi Foster was the guest host.
Actually, the surroundings weren't the embarrassing thing. Brian had on a suit, his hair was combed, and he was seated in a huge sandbox; I think there was a beach ball or two scattered about. I thought the setup was kinda cool. He introduced "Good Vibrations" with the familiar story about "dogs barking at some people but not at others." Then he started pounding away.
The bottom line was that his voice was the embarrassing thing, not the sandbox scenario. I mean, when you look back at it now, after listening to 15 Big Ones and Love You for 30 years, and being "familiar" with his circa 1976 voice, yeah, it was typical, maybe even haunting. There was something neat about this musical giant singing his masterpiece all by himself. But, to the casual fan, which comprised of about 99% of the watching/listening audience, you had to be saying to yourself - "Is that the guy from The Beach Boys who wrote and sang all those great songs. What happened to him"...