A similar thing happened to me with the stones. I ended up with the Mage Stone and the Atronach Stone, with the Ritual in the crown. I couldn't repeat it though, which is why it never made it into the final build.

I know it involved the crown, I'm just not sure how... If I can figure it out, I may attempt to stack all the stones at once

That would be a pretty cool thing to experiment on. See if the effect can be replicated. Imagine having three of any stone you want. 

I tried for hours, but couldn't manage it. It happened randomly on this character, but I couldn't repeat it on any others. It seemed to involve unlocking on the stones super fast, then fast travelling before the "x stone removed" message shows up. It basically only works at the guardian stones, where you can spam click all three.

That sucks. Something that big could have reshaped character building.

For me the process was different. I took off the crown to switch stones, thinking it would've kept the stone I had stored on it... Then I went to another stone and it gave me both active at once, or something like that. It happened a while ago. I'll experiment more when I'm able. P.S. I thought you two were doing a contest build? Haven't been able to find it, and its the one I'm most looking forward to :p

That happened to me as well, though I couldn't repeat it that way either... It definitely involves the Aetherial Crown though, and I tried everything I could to replicate it (I just wanted something pretty simple - adding the Mage Stone would accelerate levelling quite a bit, making Master Destruction much more attainable). If you do have any findings or tests you want to conduct, I can always help out.

And that contest build is coming, don't you worry... We're hyping it up (that's code for we're not finished yet)

Luckily, I have the mage stone! I've yet to switch around because so far lord, atronach, and mage has been handy, but I wanted to tuck ritual into the crown, haha. I'll figure it out, but you're more than welcome to help! And good luck with it, can't wait! :)

So some progress has been made. (My trials have been done on the guardian stones for the purpose of convenience) If you stack two stones at once, then remove the crown, you can equip the one that was stored on the crown. If you add the crown and remove it again, it will be off. Then, if you pick up another stone (with the crown off) both will be active. Where I get lost is at the third. I've managed it twice, but it seemed to happen randomly where the third stone would lock in the crown. After reading at UESP, I've heard of four stones being stacked together, but even they hadn't been sure how. I'll continue experimenting now.

No further progress, but I think I'm done for now :p