[audio bill]

I don't own the 20.7, but I run the 3.7i speakers and haven't had any trouble with blown fuses or ribbons. I play them reasonably loud at times, but never push them too hard. Typically fuses can only protect drivers by limiting the current flow and resultant power delivery, whereas if you push your amp too hard distortion can cause the driver to blow without blowing the fuse. When you have blown the ribbons are you playing them very loudly and possibly pushing your amp into clipping distortion? The amp driving Magnepans needs to have sufficient current capability into their four ohm impedance, and higher power amps tend to be best suited to driving them effortlessly in my experience without damage.