Haven't heard the Psvane 6SN7 but there 12A**7 dual triode tubes are amongst the best money can buy for a fraction of what NOS vintage tubes ask for.
Since you have the MK VIIISE to try out 12AT7 tubes, buy a set of Mullard CV4024 and report back to me how they sound, I find them to provide a very very very nice low-end.
Thanks for the tip. My inventory of 12AT7 tubes is bigger than my needs and I believe that I have covered most areas of my setups. I will consider the Mullards in the next hunt for 12AT7 tubes. It is a pity that there is no rental library for tubes :)