The head unit is perhaps, arguably, the most important part of the equation.

Think of it this way, as far as an amplifier and speakers are concerned...

If you turn your radio on to a station thats kind of staticy, you hear, that's right, static. If you have an amp and a sub and speakers and all that, and crank the volume all the way up, you're going to hear LOUDER static.

Same goes for a head unit - if it doesn't put out clean sound, all the amps, subs, crossovers, and speakers in the world aren't going to make it sound nice.

An RNS-e has enough "room" inside it to built a quality unit, and since you're obviously not afraid of spending money when you get an RNS-e, you get a nice setup from them.

This is all generalized, and I dont want to get into a pissing match with anyone on specifics... just the general idea that yes, the head unit is very important.