Elusive disc say's
"The Magic Brick concentrates 16 layers of laminated steel on an area of 12 sq. inches. This is very effective in controlling chassis vibration and the inherent nonlinear distortions associated with it. Results do vary from unit to unit, however, some of today's most highly rated tube and solid state components do sound significanlty clearer after coming in contact with the Magic Brick. "
Why not go down to your local metal shop and get them to cut 16 pieces of plate 4"x4" (12sq. inches) paint and be done with it for less then $50. hell for that mater you local wood shop could put them in a wood box for you for another $50.
That said you have to be on glue if you think having metal massed near your amp will do anything to attract stray emf. probably the mass is helping with vibration is all. seriously read about electro magnetic principals