OK, update again...
Bought myself the OEM Alpine upgrade kit...
Speakers use upgraded aluminium membranes and comes complete with tweeters amp looks pretty decent being a class d with 4 x80w channels...
Alongside that, I have sourced myself a second under seat woofer since BMW decided to be tight and only fit the newer cars with one!
Just need to find somewhere local in the North East to code into the car... :-/
Finally, I've now also bought a new binnacle cover / speedo shield to get trimmed up in alcantara to match the dash trims going in