I'm using JBL Synthesis and normally my volume is on between 20 - 30. I would like to know what is the highest volume you can turn up to with the JBL sys?
That depends completely on the music you are playing and the level the music was recorded at.
I have some CDs that sound loud at 35 and some that sound load at 55 ....
The pretty easy way to tell would be if you start hearing "clipping" coming from the speakers. If the sound clips, then you probably should turn the volume down.