JBL are not serious contenders in the modern mastering world IMO.

Names that appear most regularly at the highest levels are (in alphabetical order):

ATC

B&W

Dynaudio

Take a look at your CD collection and see which studios have mastered them. If you go to their respective websites you will see which equipment they use. There won't be much JBL (not in the last two decades anyway).

Here is an ATC client list:

ATC users

I expect that B&W and Dynaudio have similarly impressive lists.

Andrew