JBL Power Series are nice amps.
One thing i wud like to ask, is the amp hanging in air or something like that? Always install a amp on a surface where it is less prone to vibrations and has solid footing. Vibrations are not good for the PCB.
Like many members advised you, to opt for damping, good RCA cables, introduction of a nice SQ sub, good speaker wires will be worthwhile.
I wont blow the Focal trumpet here, if you are satisfied how the Diamond Sounds to you, good for everybody..!
I wud suggest you save the money that you will be spending on changing the components and use that for the installation, damping, RCA, sub etc. After that if u still are left with some money, spend it on a nice head unit or a decent sound processor.
Since you are in ISB, madhouse12 is your guy. Like all of us here, he will be more than glad to help you out.
P.S.
DIYMA is the most renowned forum for DIY car audio. Do check it out.
If you need any input from my side feel free to ask 