Run 26-5 for a low chance of 3* feeders or 10-4 for 2* feeders. Hoard.
Up enhancement skill to 10. When enhancement event comes around, feed 11 1s to either 2 or 3 to make a L10 of either.
Feed the L10s to the 6*. A shorter more expensive method would be to buy L40 4*s, current market rate is 2TE each.
Also, note that feeding a melee or a monster to a monster gives a slightly increased percentage gain than magic or missile feeds.