The Plus case actually provides better speaker options than for the original Plus. If only it were stereo you could position each speaker out of the vents on both sides of the top. However, to facilitate bucket removal without a ridiculously long cable, some kind of chassis mount to position it appropriately would be more appropriate than mounting it directly to the case.
Copper would be an interesting steampunk mod. Since the inside of the case is fully conductive it would not be an issue internally. And is unlikely to actually transmit a lethal voltage to the exterior as such voltages would short the system as it exists should they be present. Copper would also act as an interesting heat sink. I would be curious how much more heat it could dissipate over the current insulating plastic enclosure. Considering how pliable copper is, it should be used as a covering only over a more substantial (and non-conductive) framework material, like the plastic case its already in.