Help needed with e39 amp install

[sema4]

Hello - newbie alert.

Just a foreword - I understand most of the technical terms, so you can talk technically at me!

Ok, so i've installed two amps in my E39 touring, and replaced the speakers. The main amp is one (Jensen XA4100) that I got for £15 from eBay and is rubbish. The amp for the sub is a rockford fosgate punch 200.2 and i'm happy with that.

The line outputs come from one line output converter that is in the front behind the dash (this is a SoundGate LOCPRO), and the other comes from a line output converter which is behind the panel covering the left rear wheel well (there is a handy speaker connection point in there). The other loc is a 'Halfords oh-god-why-did-i-buy-it'.

I also have a DICE Silverline iPod integration kit hooked up using the R40 radio harness.

Now the issues -
1) There's quite a lot of noise which comes through the system in terms of interference. Little ticks and strange noises when things get turned on or off. I believe some of this is due to the main amp's very poor power supply, as I still get some alternator whine even with the RCA's disconnected. This is more evident through the rear channel than the front.

2) The LOC in the front is very sensitive to position... Depending on where the LOC is positioned, I get a variety of interesting noises produced.

3) The DICE unit makes a 'tick tick' noise every time the display is updated, although this is only audible in quiet periods of music. It also makes very weird noises if the backlight on the iPod is not on. I have taken the obvious route out of this, and turned off the backlight timer, but it's not ideal.

So, I have a plan, but i'd like some feedback on this.

Firstly, I think if i upgrade the main amp to one that can take the differential speaker level inputs from the head unit directly, i'm likely to get a much better result. And yes, the XA4100 can do speaker level inputs but i don't have the connectors. I'm looking to spend around £150. Any suggestions? The main amp needs to be able to have a non-fading pre-out for the sub amp.

One question I had around this - will the amp actually benefit from the differential output of the head unit (i.e. reduce the noise induced in the wires, much the same as a balanced connection for pro-audio gear would)?

With the DICE unit I have heard suggestions of putting a 2.2k uF capacitor across the power lines for the unit. Do you think that would help?

Another option I thought of was to put a good quality 4-channel LOC as close to the amp as possible. I am guessing this would be less optimal than using an amp that took speaker level inputs gracefully.

I know i've rambled a bit here, and I apologise, but I could really do with your esteemed opinions on what my next move should be.

Thanks in advance