No, Boss is showing their maximum power output, where JBL is showing their RMS or continuous output. Typically, the max power is higher than the RMS, the RMS power is more important. Also, the JBL amps are much more reliable and better made than Boss products. Also consider sound quality, you can have 1000 watts of bad power that sounds bad, or 10 watts of good clean power. I'd take the clean power anyday. You said you want it to run the four speakers and sub? If you want to amp all that stuff, you might want to consider a larger 4+1, 5, or even 6 channel amp. Those are more exspensive, or you can run two amps.
Edit-I just saw your list of questions at the end of your post.
The volume control on the amp is often referred to as a gain control. It is not a volume control, it should be set to the proper level, based on the speakers it powers, the volume of the music you hear is adjusted from the CD player. Don't fiddle around with the gain settings on the amps, set 'em and leave 'em. The preamp output is a pair of RCA plugs on the back of the radio that is to be connected to the amp via RCA cables.
