I use the AUX cable into my iPhone sometimes but the sound quality is pretty awful, it's so quiet!!, is this just a common thing with the AUX connection or could it be down to my cable?.

Not sure if it makes a massive difference but do you have volume turned up full on the phone and then control volume by stereo
You only get out of the car stereo what goes in so if the output from earphone socket on phone is low so will the stereo Nanocom Evo

It's a bit rubbish as its got a controller behind the aux input.
You can wire directly to the aux input cables, effectively bypassing the unit. Improves the quality no end.  Bodsys Brake Bible
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How do you go about wiring directly to the AUX cables?
I do have the volume on both the phone and the car up to full and it's still quiet.

Either tap into the red/blue/black wires behind the passenger side kick panel, or directly to the wires going into the back of the radio.  Bodsys Brake Bible
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Clock On The Dash/ SNOTM /3Flash / BT Update /Service Reset/Error Codes read\ Gearbox Reset
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Bodsy wrote:

It's a bit rubbish as its got a controller behind the aux input.

Easier fix for iPod- get a lead that's got the wide iPod connector on one end and the headphone jack on the other end- sound quality is perfect.