USB DAC question for neutral setup. Please help.

Hi

I have PC based stereo setup and i mostly use Flac/WAV files. My setup is fairly neutral, rather lacking on energy/excitement.

I am looking a good USB DAC in $600 price range, used or new, that can help improve the overall system and also impart some energy to it.

My top choices are Concero ($400used), Concero HD ($600used), Centrance Dacmini ($500 used), AMI Musik DDH-1($500 new).

These are the main ones, i am open to suggestions for others within this price too.

Audition is not an option so i need some help in deciding what to do?

Needs to go along with the setup and improve it also impart some energy.

Regards