Hi there. Meant to say - I got a response from Subaru UK which I've copied below. Doesn't really take me further forward. I have driven a few e-boxers and they all had the same iffy sound system so it's certainly not a problem unique to mine (I did think it would be easy to sort, mind you!) Hey ho!
Noting your comments, we are sorry to hear that your head unit’s sound quality is not meeting your expectations.
Whilst we are not aware of any latent or inherent manufacturing related issue in this regard with the Harman head unit fitted to this model, we can only suggest that you make an appointment with your Subaru dealership so that they can then investigate this concern on your behalf and no doubt in the course of this, will be able to undertake a comparison sound test with one of their own Forester eB models.