I’d say you might want to have some overlap in the different trials. Of course that would depend on how long the trials are. Say you try one brand for six weeks. After the first four weeks you start a trial of a different brand.
My idea is that you have four weeks to get used to the first brand and have some follow-up adjustments. Then you you have both Brand A and Brand B for two weeks.
Maybe Brand B is way better or way worse than Brand A right out of the box. In that case, you’ll probably know if it’s worth trying to get further adjustments on either brand.
More likely the two brands will be close to the same subjective quality. In that case you will have two weeks to switch off between the two brands and at the end of those two weeks you’ll probably have a good idea of which one you like better. That way you’re not just comparing Brand B with your memory of what Brand A sounded like.