Selecting used Stax phone and amp

I hadn't listened to headphones in years, but I recently did a setup comprised of ethernet to microRendu, USB to Ayre Codex, stereo to Audeze LCD-X.  I'm impressed with the sound, but the Audeze phones seem heavy.  I'd like to try used Stax phones and amp at a reasonable cost, e.g., around $1500 for both.  Advice on models I might look for would be appreciated.  For example, it appears SR-L500 and SRM353X might fit my cost aim, but I know nothing about them.  The source will be Roon files.

Also don't know how a Stax amp might be used in a computer audio setup.  They don't appear to have USB input, not sure about a DAC.  Might it be balanced analog from the Codex to the Stax amp?

db