Your last paragraph sums it up in my opinion.
Kevin Deal at Upscale audio thought so much of the Tungsram tubes 7dj8 that he included them with all preamps he sold. read my comments above. my 2 day experience with an expensive set of 6dj8’s was not good and they went back to Brent Jesse.
It may be that most of the issues we are all having here are from running NOS tubes that are not 12 volts.
With regards to keeping the unit? DO IT, DO IT, DO IT. it is a great sounding unit with great functionality. Since mine went back to PS I have been using the DSD DAC as the preamp, and it really sounds good. But, there really is no comparison in that the preamp adds so much beauty and richness to the sound that i could not really ever choose to not have it. There are some really fine units on the market, but almost any unit that will sound as good will be more expensive and not have the value of “made in the USA” and the support of a great CS dept.