Originally Posted by Technic
The only difference that I know of is that the HD900/5 was a Marine version, the HD600/4 (one brand new and the other used) were not.
I asked the customer to swap 600/4 to see if anything changes.
It sounds to me quite decent, until attention is paid to the imbalance in sound level between the front and rears (fronts are the EPS 4ohms, rears are the rear/sides in parallel =2ohms). I have not found such an imbalance with any of my 2 PDX installs with the exact same OEM EPS speakers in the same exact configuration.
The one HD-600/4 I came over with was NIB from JL. I did switch the amps (HD-600/4s) and I got the same uneven power output with the 2ohms vs 4ohms!