Ok, I have 6x9's amped by a 100WRMS Jaycar amp.

Does this mean that the signal from the HU is increased by 100W?
Or does it mean that it is increased to 100W?

In other words,
If when it's all set up and turned up to a level that is just before the speakers are distorting, and the signal is coming from 4x45W HU; if I buy a new HU (4x60W) will this ultimately mean that the speakers will go louder, or just that the amps have to do less work?

Cheers

An amp will only output what it's max is, so you cant have an input of 50w, amp producing 100w, and have an output of 150w.
But depending on how your HU to amp is setup will determine whether you will see an increase in quality. If your HU is connected to your amp via speaker outputs/inputs, then yes having a higher output wattage will sound better, but if you just have them linked via RCA, assuming both hu's have the same quality RCA output, having a 50w or a million w HU will make no difference to the output. Only if one was a higher quality hu than the other.

This is my understanding of it anyway, if it's wrong someone is welcome to correct me :).

If your head unit is 4x45 and you coonect it to the Amp Via RCA's, then your Headunits internal Amp is by-passed, Depending on your Headunits RCA Voltage Output will depend on how loud you can set the amp
The higher the RCA Ouput voltage will mean the amp can work better..
So if you have a 2-volt RCA Output then the 100W amp may only put out 70W of clear signal power
4Volt or Higher will result in the amp being able to put out 90-98 Watts of Clear music power..
It is a bad Idea to run Amplifiers at full gain.. 3/4 of max is about right..


Be carefull of what an Amplifiers rattings are as a 2000W amp may only have about 80Watt RMS of power..
RMS is is the only guide you should use when buying Audio gear it is continous output over an extended period of time, usually 24hrs
..
PMPo is Peak Music Power Output, How much Power the amp can produce just as it blows up, so it may only produce that power for half a millisecond..

The amp I have is definately 100WRMS, so that's ok.

Atm, it's set up from the speaker outputs, to a high-low level converter, then down RCA's into the amps.

So basically, in order to get more noise I need to get amps with a higher RMS wattage after the HU?

Replacing the Head unit with one that has at least 4-volt RCA outputs with Front Rear and Sub Outputs then replace the Amplifiers with Higher Power rated ones.. 100W RMS is a fairly good size to use for your front and rears, but buying another one and Bridging it for your subs will give you more noise

Speaker line outs to RCA converters put out about 2-Volt so they are an OK signal, but getting a head unit with a 4-Volt RCA output will allow a cleaner signal to your amps allowing you to turn up the amps a little higher with less distortion..

What would the Pioneer DEH-P1Y HU be like?
I'm looking into a few of those atm... *fingers crossed*

What would the Pioneer DEH-P1Y HU be like?
I'm looking into a few of those atm... *fingers crossed*
very good quality head unit. highly recomend.
:P