Hi Eric, did you succeed in detecting the other displays? I have a related/similar problem: my OS (ubuntu 18.04) insist in not using my graphics card (firepro w9100) and would be interested, if and how you solved yours.
- What is your OS?
- What are the exact model of your HP monitors?
- What do you mean by Single Mode MDP adaptors? Are you referring to miniDP-DVI Single Link adapters? If yes, are they passive or active?
You can only use up to two passive adapters with a W9100.