"Thanks for your mail. I have not tried the 6N5P yet. Looking at its specifications, it should work in the Stratus however the gain will be reduced, which could be beneficial with very sensitive headphones like the Utopia and TH-900 for example. I will try to order one and test in the Stratus and report back. Merry Christmas and happy holidays to you and your family too!" This is my reply from Mr. North.