budget diy tube preamp beating many expensive preamps... problem with my system?

It could possibly be the cables. I wonder why you bought cheap ones when you spent so much on the rest of your gear.

It's not the cables, it's the simple circuit design and the use of the 6v6 tube. These types of tubes in a preamp give a big bold sound with better air and instrument separation in my opinion.

@invalid what would be an upgrade from this then

I will eventually get better cables. Tbh the Amazon rca cables I have seem better built than my custom tedd allen cables.