I heard the 380's yesterday. With very little play time they already sounded great. They were driven by a Hegel 590. The sound stage was very wide. The speakers may have been almost 10 feetaapart but the sound still went beyond the speakers. The horns were what I was hoping, nicely extended and dynamic with no harshness, cymbals and piano remained smooth. More in line with the 4367 than the Studio .
The bass was plentiful but remained in it's lane. However, I expect if similar to other JBL Synthesis the bass will be more refined with some break in. The midbass was hefty. My 4367's were as well before break in, now the bass is crazy accurate, especially from what one might expect from a 15" driver. The 380 has three 8" drivers. With the 590 the bass filled a large open room. If I'm wrong and the bass should happen not to change, the 380 would have more of a classic JBL bass. But, I'd bet the bass improves even more.
A note worthy experience, my friend played a couple Classical tracks, I was absolutely impressed. With the transparency and control of the 590 and playing the 380's it was like I was at the symphony, the openness and air lent to the tricking my brain. I really enjoy when that happens. The combination was dynamic with no compression or distortion.
I think if the word gets out on the HDI series and they are where people can hear them JBL will have a hot item.