@mceljo I have upgraded the tube to a Western Electric 396A that I paid about $90, but I don’t think that I can hear a definitive difference from the GE tube that it replaced.
By chance have you tried using better digi-coax cables? The GE and Tesla tubes sound notably more transparent compared to the WE396/2C51 tubes in my own MDHT Labs Orchid DAC. The WE is much less transparent, a bit more veiled over in some systems, and so much so that I really cannot use it in my all-tube system. Maybe yes with a more detailed SS amp/preamp setups like I had years ago. I’ve tried four different digi-coax (Cardas, Analysis Plus, Audioquest, others) and was suprised to hear a difference with DAC tubes after advancing to better Digi-Coax. Ended up with an OCC copper digi-coax cable for the stremer to DAC, and OCC interconnect cables again from the DAC to my preamp. Now i notice every single tube change in my DAC for better or worse.