I never heard the Erlkönig, but from what I know about VE's sound I expect those will have a more conventional tuning then the Thummim. Joseph explained that they wanted to do something crazy out-of-the-box with MMR and the Thummim embody that unmistakably. They are unique with a genuinely spherical stage (sounds seems to come from every direction), a heavily coloured tuning with gobs of energy and yet they manage to produce a very high level of detail and texture. The term "marmite" comes to mind once again. They are completely unique and amazing if you like their sound, but can be off-putting if you don't, especially if you demo only briefly without adjusting to them. I love a good marmite IEM and am really enjoying these now, but if I had to put my own money down I would go for the Erlkönig. In part that has to do with the fact that I don't like the Thummim for classical music and I expect the Erlkönig will be a lot better there. I would be curious though to see how the Erlkönig would stack up against the Dream XLS for classical, as I think the Dream XLS do phenomenally well for that.
On a completely different note: Our puppy was born yesterday!