I own the JH-16/J3a. I do listen to the JH-16 without the JH-3a.
coming from a musical background. There is a slight bump in the lower frequencies but it is slight. Only matters in rock, pop. Under classical it is not used much. Except for some pipe organ music and piano.
When I listen to Izthak Pearlman, Yo-yo Ma, Pepe Romero, Paco De Lucia, Paco Peña, Manuel Baruecco, Andre Segovia, John Williams, the master editor in Christopher Parkening (and catch all his editing prowess), Kazuhito Yamash i ta (one word but the censor nonesense stricks the players last name), basically every string player that is great, under the JH-16. The insturments are unmistakable. Each has a certain sound signature that when there is any tuning done on the IEM/speakers etc, always change the instruments sound signature. I have heard many (save for Andre Segovia) live and that sound always sticks with me. To include when they do there tuning (440 hz for Classical guitar). The JH-16 nails it.