The RFI thing isn't as dangerous as it sounds. I am only running 1 to 25 Watts and my antennas are matched (SWR very low). I am meticulous about this and have had the radios on spectrum analyzers (radiating trash RF is sort of like refusing to bathe -- tough on friends and neighbors). It looks like the particular speaker system is very susceptible. It is a SoundWorks system with a subwoofer and amplifier. It is further from the radio gear than the other sound system, which only makes a slight whispering noise when I transmit data.
It is fairly common to run across a device that won't reject radiated or out-of-band RF. (I could tell you stories.) The FCC doesn't require much in the way of RF immunity. The premise is that it would be too expensive to require all electronic items to be robust in radiated fields. Instead, manufacturers are required to meet less stringent standards and then required to repair equipment that malfunctions on a case-by-case basis. Most consumers have no idea of their rights in such cases. The normal reaction to RF interference is to blame the radiator. At the same time, look how hungry everyone is for wireless electronics.
Well, I was guessing that you might have some first hand experience with RFI and computers. The ferrite cores are expensive and it would be nice know what was the best thing to buy. I will try to get back to this post with some info so others might benefit.
By the way, I am very impressed by how you take on all comers here. Also, this is the weekend to sneak the new motherboard and all the rest into the old case. It will be another adventure for me. I don't do enough of this to ever be good at it. Have a fine weekend.