Audio Research Pre-Amp advice

I would love a 28SE if I could find used at a good price. I just want to buy the best model in my budget of around 6k or less. Don't want too old because of service issues. I am just trying to find the best one within budget. I am not sure which model sounds best that's why I am asking people who have had experience with this brand. Thanks for your responses.

Add one more for the LS28SE, I have had mine about 2 years and am very pleased with the performance. I did have a REF5SE and it was a great piece, long story short, I tried solid state and bought the LS28SE and really think it is so close to the performance of the REF5 and way less heat produced. 

I have an Audio Research SP-16, which I recommend due to the tubes used. This pre-amp uses 12AX7 tubes which are inexpensive, and many brands make them. It also works flawlessly with most amps I have - it is also only single ended though.

There’s an Ls28 for sale on eBay for $5500. It doesn’t say SE. A little over 1000 hrs on the tubes.

Thanks, I saw that but don't like to deal with ebay. I would rather buy a demo from a dealer if available and I am looking for silver color.