Buying a used Pre-amp...Advice needed

I'm looking to buy a used pre-amp with a good sound. Here is my stiuation. I've been buying several DACs to compare them with my existing system and really amazed by how differences in sound each DAC makes. But I discovered that my Chiro C-802 DTS Processor do not have analog pass-through. That's mean, it convert analog to digital and then convert the signal back to analog again(Correct me if I'm wrong). So, while waiting for the Processor to be modified to get analog by-pass, I want to get a good pre-amp to listen to the music.

Now I need your suggestion for a used, good sounded pre-amp. It should not be an expensive one (around $400 used). Thanks in advance for your help.