I don't have experience with good tube preamps and want to avoid them due to maintenance, microphonics, noise, distortion, and power usage. I just received my benchmark HPA4 and have been pleased so far. The clarity, imaging, and wide bandwidth are amazing. 30 day money back and the HPA4 is $3300 and the LA4 w/o headphone is $2900. I came here to say that PCs and fuses can help you tailor the sound, even with these types. Look at the rest of your system too. My next stop in a guest for warmth with all SS, all digital is the wall outlet. I have Furutech GTD-R which has a bit of U shaped EQ, and was suggested to use SR Purple or Audience outlets.
Maybe some heavy McMasters felt glued on the front of your large floor standing speakers would help with imaging. Like old Dunlavys or Wilsons. I plan to try that with my psb platinum T8 towers.