Not sure you really need a back up 6111 tube. I sure ALO Audio would have a supply of these in-stock. Also in their literature they do mention because of the rated life of the tube, replacement is non issue.
I am using the Continental V3, with an iPod 5.5g with the RWA iMod. Using IEM it has absolutely no hiss, dead quiet, even right out of the box.
It did take a burn in for either the iMod or the V3 to come to life.