What I have found to work best for me is to bring your X5 and E12 or E12A with the stacking kit to Best Buy (or a similar type store) and look for the smallest camera bag that will hold the DAP and amp and make sure that it has a loop on the back for our belt. Look for the bag to have two zippers for the main compartment that you'll carry the DAP and amp in, this way you can unzip just the top to have access to the headphone output and the volume control on the amp. Amazon has a ton of bags like this, but you may have to try a few before you find the one that works best for you.
I recently bought this one: http://www.amazon.com/gp/product/B00DUGZEWK/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1 (I remove the shoulder strap)
The size of the bag is perfect, BUT I didn't realize that it only had one zipper which means that once you open the bag to plug in your headphones the top and side of the bag are left unzipped (the zipper doesn't go all the way down the side which is good). I doubt that the opening is big enough for the stack to fall out, but it would be better if the compartment had two zippers for a smaller opening only at the top. At this point, I have a few bags that I use and carrying the smallish bag (outside measurements of 5.75" X 4" and 2" deep) on or near my hip has worked great. It's easy to lift the gear out if needed, easy to make adjustments while in the bag and most of these types of camera bags also have room to store your IEM's. I've read that at times these type of bags vary in size just a bit so it's always best if you can try one in person.
I'm sure that there are other ways to carry your stack, but I prefer this way as I'm not running the risk of sitting on the gear or putting too much pressure on it and thus far its worked great for me.
