JBL amp

JBL has R&L FIXED LEVEL input from head unit. Using commands from MFD/Head unit, it regulates volume, EQ, balance and fade digitally.
JBL has 7 outputs:
Right and left front midrange output. Not sure if these outputs have high frequency rolloff.
Right and left front tweeter output. These outputs DO have low frequency rolloff.
Center speaker: mono output, with limited midrange.
Right and left rear outputs. These outputs have no filtering, other than the general EQ.
Filtering, EQ, balance, fade, and volume are digially processed, which is why some feel the sound feels as if it was overly compressed.

There is a thread somewhere here that has frequency response analysis scoped out.

 

That thread can be found here

There is a post on the second page that speculates based on the avi's that the front mid/bass outputs have low pass filtering, with only the rear outputs being full range.