This post is about the Yggdrasil in my system, and separately about the New Sensor PX300B. Before adding the Yggdrasil, my system consisted of: Marantz SA8005 > Dyanco PAS4 (recapped by me) > 300B amp (refurbished by me) > Zu Union speakers + REL sub. I had a Bifrost Uber that I upgraded to MB and added it to the system (via coax from the Marantz). The BiMB beat the Marantz when it comes to staging, but didn't have the dynamic range of the Marantz. Particularly, the lower mids were lacking in the BiMB. So some recordings sounded better with the Marantz directly feeding the preamp, and others sounded better with the BiMB. I really wanted to try out the Yggdrasil, but was hesitant because I thought it would share the same sound signature as the BiMB and of course the price (at retail it's more expensive than any other component in my system except possibly the amp). With encouragement from @zerodeefex, I went ahead and bought a (used) Yggdrasil. The Yggdrasil combines the best qualities of both the Marantz and the BiMB and beats them. It is so good, that that Marantz is no longer connected to the preamp, just to the Yggdrasil through RCA coax (and I thus ditched the SACD layer of some of my music). Music sounds like it should through the Yggdrasil. On to the 300B tubes. I've tried many 300B tubes including: Chinese punched plate, JJ, Western Electric (new production), EML 300B, and the New Sensor "Gold Lion" PX300B. Originally I only had the Chinese and the JJ tubes. Then I bought the PX300B. Right after they arrived and before I even had a chance to try them in the amp, my friend offered a pair of WE300B and a pair of EML300B for a combined price that is unheard of (really). I couldn't pass up that generous offer and picked these up. Yes, the WE's are awesome, and the EMLs extend more in both directions, and I was loving them. Then one day I decided to try out these PX300B tubes sitting on the shelf. They had some of the delicacy of the WE and the neutrality of the EMLs. After some hours on them, they sounded even better with the bass gaining more prominence and the treble more sparkle. I don't know how many hours I have on them now, but I haven't removed them from the amp since. The Marantz/BiMB/Yggdrasil impressions above were all done with the PX300B. These tubes are excellent (but give them time to break in), and at $330 I would recommend dropping the desire to obtain more expensive 300B's. That's it ... hope people find this at least slightly helpful.