Step 1 : make flat mystcraft world (adding dungeons page would help too, but not essential).
Step 2 : make 2 soul shards and kill 1 zombie and 1 skele with the soul shards on your hotbar so you have 1 kill of each in each shard.
Step 3 : go to mystcraft world and go exploring. You are looking for 5 TC barrows and as they are mound shaped, they are really easy to find.
Step 4 : right click the shard on the spawners in them until you've done 4 barrows. In the 5th barrow kill loose skeles and zombies til you have 824 kills in each shard then break the spawners with your shards. Now you have 2x tier 5 soul shards.
Step 5 : make another soul shard, go to nether, find 1 wither skele and kill it so you have the kill on your shard.
Step 6 : get yourself about 10 XP levels.
Step 7 : go to your anvil, put wither skele shard in 1st slot, put one of the tier 5 shards in the 2nd slot, collect tier 5 wither skele shard.
To get the actual skulls via an automated method, what I've done is make a standard 7x7 enclosure and soul cage, red alloy wire, lever etc, but I've made a 9x9 ring of mystcraft crystal portal at the bottom which links to a place in mid air above a 3x3 crystal portal in the nether, which in turn links to a 1x1x2 glass enclosure back in my overworld base. For those that haven't already figured it out, what happens is the soul shard spawns the w/skeles and they drop into the portal, get teleported to the nether then instantly fall into another portal which brings them back to the overworld into a 1x1x2 enclosure. Of course, on the enclosure I have my melee turtle and XP turtle on one side and a brain in a jar on the other side for any 'loose' XP needed. Fully auto, no lag, and after about 3 full days of running it I have 81 stacks of wither skulls.
