Those are the ones!
This is what I posted from my Axpona thread about using the PX-4's:Enter the KR AUDIO PX-4 DHT
On Friday I was using SV811s (a show favorite with the SHL5's), but on Saturday morning a customer
surprised me with a new pair of KR Audio PX-4s that he just bought the week before and has fallen in
love with. He was willing to let me borrow them for the rest of the show if I liked them, and I couldn't resist
trying a new DHT with the LIO.
Not an inexpensive tube (~ $800/pair ?), but they AMAZED us all!
These tubes have the rich midrange of the SV811's, but with a more extended top end and more solid bass, . It was
a tube that could play rock, jazz, classical, electronica... all equally well and left some LIO customers who visited wanting
to get a pair for themselves (myself included!).
These tubes run on the 4V filament setting
and only draw 1.1A of current each, so they run fairly cool
and should last a very long time in the LIO DHT PRE circuit.
So it looks like quite a few of you guys also have them (or they are on their way to you). Enjoy them!