***UPDATE***
So waited around being patient for one to come up online for a reasonable price, then last week one came up on an auction site with no guarantee whether it was working as it was taken from a scrappy. I'm a gambling man and put in a bid and low and behold i won it for.......£26. Even more sceptical about it actually working until it came yesterday and plugged it in. Boom! I have sounds!!!!
Just to clarify; my Z4 is a 2005 and this amp was from a 2003 so was as simple as plug n play. I only mention this as i've read that some people have had to flash the firmware or something....
Anyway, onto the next down the list of problems: 1. stopping the water ingress in the boot, 2. handbrake non-efficiency, 3. bonnet cable and 4. dreaded DSC/handbrake amber lights.... fun times.