Hi
Re your volume issue, I think some Z3 have a separate amp fitted, which if faulty may explain the fixed volume level not being cured by a new head unit.
Anyway, my reason for this PM is that I have been looking for a stock radio as mine is a cheap modern unit fitted by a previous owner. Hence if you are interested in offloading one I might be interested in it.
Hope you get the fault sorted.
Kieran