I've got the previous Freya and went from the stock tubes, then to the Tung Sols and landed on the PSVane. I got them off Amazon of all places and it added a bit better sound than the Tung Sol and over all I'm really happy. I had to grind the tube opening a tiny bit with a dremel but it was worth the short effort for the better sound.
https://www.amazon.com/Matched-Psvane-UK-6SN7-Vacuum-Tubes/dp/B00N9T5ZHW
https://www.amazon.com/Matched-Psvane-UK-6SN7-Vacuum-Tubes/dp/B00N9T5ZHW