OK, so this is likely to be the only modification I ever make to it but I'm happy with how it worked out.
There's now a miniature toggle switch by the headphone socket which switches the speakers on and off. Not a major change but this means I no longer have to mess about plugging and unplugging the base unit for my wireless headphones.
While doing this I discovered that you only need to switch the 'sleeve' connection on the jack socket, not all three. Not that I imagine anybody else in the world will ever bother doing this. I only did it because my speakers stopped working.