I am presently using a pair of cheap Trust SoundForce 2.0 computer speakers bought from the local Wilkinson store with my K3. I originally bought them to use with the JUMA since Gerd, who built it, hadn't included an internal speaker. However I tried them with the K3 and found they were a substantial improvement over the built-in speaker. With several turns of the input cable wound on a clamp-on ferrite choke they are almost immune to RF breakthrough even at 100 watts. However, they look a bit cheap, I felt that the sound quality could be improved, and I would be happier with no RF breakthrough at all. Unfortunately I couldn't find a way to get inside the speakers to install extra suppression components. Although two Philips screws are visible at the base of each speaker, the case halves also appear to be secured by screws at the top which are behind the grille, and I can't see how to get that off.
I saw some Logitech S120 speakers advertised on eBay and decided to order them, as they looked a lot nicer, and matched the K3 better, and since they came from a "quality" brand I thought their RFI suppression might be better. The speakers arrived this morning, and are already back in their box to take to the local charity shop. The sound quality was better than the Trust speakers, but I was dubious about how they would perform in the presence of RF since even before I transmitted I could hear a faint pulsating buzz - possibly caused by a DECT telephone base station nearby.
The RFI was so bad I got a loud buzz even on a tuning signal of 6W on 15m. When I pressed the mic PTT with 100W selected the resulting burst of noise almost caused a need for a clean pair of underpants! I can see no way to get inside these speakers at all, but even if I could, it would probably be hard to make them RFI proof given that the susceptibility is so bad to start with.
My loss is the Oxfam shop's gain - and yours, as I decided to post this as a warning. Logitech S120 speakers should not be used within 100m of a radio transmitter - at a very minimum. I just hope that none of the neighbours is using them.