@xcool "... I’m sure I’ll get that itch one day to try out some tube rolling, but I know very little about it. May I ask you what tubes are you currently using?"
Yep, with your fairly new preamp and burn-in going on, maybe save the "new tubes" idea for a next-chapter. Those stock EH tubes will get you through preamp burn-in cycle to start. The tubes I’m using (now) are not vintage NOS any more. I keep those hoarded away. Finding matched pairs and matched quads is difficult, costly.
There are various, and availability changes by tube seller and the best recommendation is to call a reputable tube seller who offers a guarantee.
For NOS, was previously using a tightly matched quad of Sylvania Black Plates, mid 60s, and past few years using new production TJ Full Music 6SN7s, and awaiting some of the latest PSVANE CV181-TIIs, soon. I missed out on the good Shuguang’s a few years back. Note, again, a good tube reseller (specialist) is where I’d start since you are new to this, when u are ready. Brent Jesse, Andy at Vintage tubes, Jim McShane are a few to note for vintage stuff. I’ve given up on vintage or NOS 6SN7s, rare, few matched pairs/quads out there, and way too costly. New production here forward. Best of luck.