Used Pre under $8K with lowest nosie floor(?)

My BAT is quiet as a tomb. I'd also look at an ARC Ref 5SE or, if you can find one in your range, a Ref 6.

If you buy used, you can get an Ayre KX-R (non twenty).
I just got one and even though it is only a few hours running, I can say it is unbelievably quiet.
For tubes, an Atma-Sphere MP-1 or 3 used should come in around $8K.
In fact, I will probably get an MP-1, myself.
Bob

My Ayre k1xe is quiet.....even with the volume up on phono, ear to the speaker.....nuttin.

Spread Spectrum Technologies (SST) Ambrosia.... Find any review,  I've sat in front of this and compared with many.... Around $3000 used around $10,000 new or $7500 new without phono.  Excellent phono by the way,  Excellent headphone amp,  balanced and single ended, tone controls, excellent remote and quiet as a tomb. 

My Supratek Cortese is silent.