I suggest you search out the thread titled preamp deal of the century on this forum. It will help you learn about the supratek preamp which is right around $2,000 and the Don Sachs SP preamp and the ultraverve preamp. These are all tube preamps and are universally praised for their sound.
Almost embarrassed to ask, but...
I’m seriously considering a high(ish) end used pre amp as my next upgrade. Currently using Marantz AVP, and looking for the next step up in sq for 2 channel. I have an Oppo UDP205 for discs, but also use a lot of streaming music. The Oppo has the DAC, but I’d need to get the streaming music into it. From the Oppo I’d take analog out to the pre amp. I can use a tablet, but I’d prefer a stand alone unit plugged into the Oppo. Also, what is the best connection for digital output of the streamer to digital in on the Oppo?