Gregm. Because neither the Corian or Perspex are totally neutral, you may get the best result using Corian on the source (and maybe also preamp) and perhaps Perspex on amp. Mixing different shelf materials together will hopefully avoid any too obvious resonances. I found Corian everywhere to be something of a problem. By the way I did find Maple Butchers Block to be OK too - it sounded slow and murky, but not nearly as much as MDF did. It was able to be improved with cones. I mention it because it may be OK with the very heavy stuff and provide still more variety to your tuning of resonances. I believe you have got my point on the steel wire - it sounded very much like there was a steel stringed guitar playing along with the music.