I am looking for used speakers with a price around $750 or less. That have open, detailed with very good imaging and that are small monitors.
This sounds like a descriptor for Silverline Minuet Supreme Plus speakers at $699/pr new. I heard Alan Yun demo them at a NYC show with (literally) a cheap-ass garage sale DVD player and Monarchy electronics, and it was one of the most jaw-dropping experiences I've had in audio. That modest little system faithfully and visually reproduced a 3D standup bass in a fairly large room in a way I'll never forget. And they're cute, small, and attractive as hell in rosewood. And that was the first version Minuets. I'd think your Threshold stuff would make them absolutely sing. What are you waiting for???
The others that pop to mind if you can find them used would be Nola Boxers, Joseph Audio RM7, Reference 3A DeCappos, or some ProAc or Totem monitors. Best of luck in your search.