Seems to me that metal, a very good conductor of heat, would be a very bad idea. Eventually almost all of the heat will pass through to the wood - and when it gets hot enough, it'll burn, which would be A Bad Thing (tm).
No, it seems to me that a thermal insulator would be a better idea than a thermal conductor. I'd use something like high-temperature ceramic tiles, high-temperature millboard, calcium silicate board, or silica board. I'd say that silica board (
http://www.mcmaster.com/catalog/108/html/3209.html for example) would be the best option, although it's quite expensive. Then again, so is replacing burnt cabinets...