Just a little correction about Sophia Electric and KR Audio Electronics. Sophia Electric is US based company, which tubes are made at TJ Full Music factory, Tienjin China. KR is Czech Republic based valve and amp manufacture, which been and are made in their own factory in Czech Republic.
I am wondering how many hours you have had with KR's please, cos, usually, they need around 200 hours of burn in period.
The second stage of amplification is provided by one PX4 tube per channel. The PX4 dates from 1928, and was developed by the English outfit Marconi Osram. There is almost no NOS market for it, and only two current replicas - Sophia Electric, and KR Electronics, both manufactured in Eastern Europe.
For some aberrant reason I always thought Sophia and KR were the same firm, and therefore the two tubes were the same, but fellow Head-Fier bdh set me straight, for which I thank him. I got a pair of KRs to compare with the supplied Sophias, and found that the Sophias sounded significantly better