I have speakers: http://www.kef.com/KHT/KHT2005.2/gallery.htm No biggy, but i want to mount a couple of them on a steel cabinet. As the Air Force would not like me messing up their cabinets, I was considering using magnets to mount the speakers. My question is, do they make magnetic strips strong enough to hold the speakers, maybe four or five pounds tops, and would such a magnet also interfere with the speaker?

I can't give you a detailed physics answer, but I would be very hesitant to use large
magnets on the back of the speakers to mount them. The magnets used in the drivers
of the speakers depend on free movement to generate accurate sound waves. I would
be concerned the additional magnets would impede this movement, causing distortion.
Could you use large velcro strips with the peel off backing instead?

You'll probably find that the steel cabinet has a resonant frequency and that certain bass notes will make the whole bloody room vibrate, or at the very least make the music sound utterly awful.

You need to be careful what you attach speakers to. Plywood is popular because its very nature of crossing grains separated by glue makes it very dead acoustically.

Velcro might work, at least it provides some acoustic dampening between the speaker and the metal. If you can try it out without spending a lot of money it's worth trying.

I think I could get away with an adhesive, what if I put some thin foam between the speaker and the cabinet door?