Welcome to the forum.
Regarding your Shuberth saga allow me to add some points; the warranty is in fact worldwide (not US and Japan, not availiable in those markets), but the product each time should be returned to the selling pooint, it is written in the instructions and warranty leaflet. Vendor is responsible to make all arrangement , inspection, pachaging and shipment on the customers behalf. Do not believe that has something to do with EU, on the contrary . The local shop any local shop if wanted to really assit could provide all services and return the lelmet on your behalf using the internal supply and support line , but as you state they limited their support in instructions and demonstration of good manners.
On my next trip to UK this coming June will bring with me a pair of speakers (fm an Interphone set) that can be used with the Shuberth and were tested before in a similar situation. They are availiable free of charge , collection is an issue since I would be in Lester (Leichester) but if you're interested it can be arranged.