Tubeyist sounding Pre-amp?

I DO agree with everything you said bpoletti as far as it went. What I have personally found however is that some components characterized as neutral/accurate are really, to my ears, not that at all over extended listening. When fatigue comes into play on a regular basis there IS distortion. The word neutral in audio is overused and almost irrelevant. It is only neutral relative to what one is accustomed to. As Rodman notes it ultimately comes down to listening preferences over accuracy or lack of.

Keep on hearing great things about Keith Herron’s gear but have never listened in a familiar system but one always on the radar.  " Correct presentation in time is the key element to transparency." Keith Herron. I definitely agree with THAT statement and have found it to be so true in my experience.

Cant get much for $500.00 maybe a 40 yr old CJ.Good luck let everyone know what you get.

At $500 for a tube unit, I'd think more about condition than sonics.
Also, with your amplifiers rather low single ended input impedance, it might narrow your most likely to be single ended output tube preamp options. Not sure if you need a phono stage, that'll probably add to the cost.
Here's a quick off the top of my head shortlist of inexpensive tube pres,
caveat: don't know it they'll work with your amp, or if any fit any of your criterion, but at $500 you're not going to get too many options:
Cary SLP 50
Conrad-Johnson 10
EAR 834
Quicksilver Line Stage
VTL TL-2
I'm sure there's more,
good luck!

the $500 figure was my guess at a repair to my SF Line One - it is at a local shop now and I have heard nothing for two weeks.

I have to admit I have my eye on a piece of ARC gear too, tho I understand they are very neutral sounding...

$500 to repair SF Line One is a very large figure. 
$150...200 should be about right -- $120...150 labor and about $50...80 parts