The guy came back today and ultimately the options he changed weren't very complex but it seems odd that the default settings produced such poor results - presumably the same settings exist on the windows driver, but are configured differently? The printouts from Windows and Mac are now pretty much identical.
In case anyone else finds this thread and has similar problems - I'm trying to translate the options names from French so it might not be quite accurate.
The settings were all under 'Quality' on the mac driver, the first setting is 'Vectorial' or 'Frame' (?), the Frame option was significantly better, and faster. The second thing that made a large difference was Smoothing, there are 3 options for this, one for Grey Smoothing under advanced, they should all be turned off.
In any case, it is just a question of finding the right settings in the driver options, thankfully!
Thanks everyone 🙂