OP said:
"I have 2 SVS subs, the DB4000. I adjusted the cross over and volume which improved the bass. When I put my ear next to the bass driver of the JBL at 50-55 db there was very little bass to be heard, in a piece that had substantial bass.
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The bass (and more highs) were there, but your ears are insensitive to lows and highs at low volumes (relative to mids).It thus could only be heard if you BOOST the bass and BOOST the highs to compensate, not for the speakers, compensate for your very common ’low volume insensitivity.
Again, IF it has too much bass at low volumes, it would sound bloated at higher volumes.
Perhaps someone should design some speakers with a frequency response specifically for low volume, but they don’t yet exist IME.
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My speakers have 2 L-Pads (both my main horn speakers, and my office AR-2ax, and my Garage/Shop (also AR-2ax).
I adjust, in my space: the mids to the woofer, next I adjust the tweeter to the mids (using an SPL meter on a tripod, at ear level at listening position), using a CD with 29 1/3 octave test tones. For my preferred listening volume which is higher than yours. Then, I make the PREFFERED final adjustments, BY EAR, but do not push the highs too much (I listen with younger friends often).
YOU, IF you had L-Pads, could adjust BY EAR, at your low volume. IOW, make a speaker with a frequency curve that fits you in your space, that is afterall what you are after.
You will NOT find a speaker without controls that will do that for you, in any space.