ah yes ... the trade in does make a difference.
Some good photography in your gallery and some nice components.
Have a look at the insert in your box [if there is one] which has a stripped thread. You might find you can simply push it out, from the front using piece of rod and get a replacement from Bunnings [or similar]. The main problem is probably going to be access and not damaging the drivers while doing the job. I'd be a bit inclined to take them out for safety regardless of who you get to do the job.
Otherwise ... yourself, or the nearest person you can find in the Yellow Pages.
Sydney, for anyone wondering.
jules