Bryston - Because You Want Extraordinary
I recommend taking a step back. It sounds like we are trying to come up with the tag line before we identify what the brand stands for. In other words, we are doing it backwards.
I recommend the digital equivalent of a whiteboard session with both your employees, dealers, and customers. As each of them what Bryston means to them, or what adjectives they would use to describe Bryston. Once you have that foundation, you can try to use that knowledge to develop the tag line.
There are additional benefits of doing this. 1) You will see if there is alignment internally in your org. 2) You will see if your customers are aligned in their opinion of Bryston. 3) You will see if there is a misalignment between your perception of Bryston and your employees, dealers, and customers, which in itself is good to know, if case you need to address concerns.
Some of the adjectives that were already called out were "engineered, quality, customer service, and audiophile."
If you do ask for the feedback, I would not bait the employees, dealers, or customers by giving them example words. I would ask them something like, "When you think of Bryston, what comes to mind? How would you describe the brand or products?" In other words, you can ask for more details, but I would avoid guiding the answers, because you can create a bias in the response.
Also, you may want to brace yourself for answers that you did not expect or would rather not hear.
P.S. In case you were curious, I have experience in this area.