I've done complicated, now it's time for something a little more …elegant. In my SSP, I've got an MFR harvester feeding oreberries into my AE system, which is set to export them directly to the smeltery intake enderchest. When it fills up a bit, all I have to do is go push a button to feed the dregs back into the smeltery & start the next metal casting. The liquid transfer node seems to hold a full stack of ingots worth of molten ore & will fill with the next layer as soon as it empties. If you have several different things in the smeltery, the drains will pull from the bottom layer.
Here is a cleaned up & refined version built in a creative test world.
Here is a cleaned up & refined version built in a creative test world.