Preamp for a Line Magnetic i518?


I am interested in adding a preamp to my system. Currently using a Line Magnetic 518 integrated 845 SET. I listen mostly to vinyl with a Chinook phono amp and VPI Prime turntable with Lyra Delos. Speakers are PSB Imagine T3. Any thoughts on adding a preamp and suggestions? Partial to tubes but let me know if there is any ss that would possibly be a better match? Budget approx $3500. I appreciate any/all advice....thanks.
ekimg
ekimg,

I use NOS Tungsol 5751s in my 518IA; I prefer the slightly lower gain of the 5751 vis a vis the 12ax7
facten...thanks for the info. Obviously the 5751 is compatible change for the 12ax7?  What is the benefit for lower gain in your opinion?
I am suprised that the LM518IA will drive the PSB Imagine T3's. I believe it is rated at 22 watts. I am running Shindo Aurieges pre and I tried a Will Vincent Baldwin Amp which I believe is at 25 watts and I felt it was very much underpowered for the PSB's.
I have a 518ia and am considering an external preamp. But if the direct input only bypasses the pot and not the preamp section, would another active preamp only cause harm? Maybe The best scenario is a good passive preamp with a better attenuator?