Hi Rich,
PTN3460 was designed/tested to work with multiple GPU (Intel, AMD, Nvidia) in Windows or Linux platform.
We had no customers using PTN3460 with sort of HDMI to Display Port converter in Windows OS and never tested such application.
The issue might be related to incompatibility issue with STDP2600 proprietary device driver running on Windows OS, and we only support standard DisplayPort driver which are provided by Microsoft for multiple GPU (Intel, AMD, Nvidia) in Windows OS.
Best regards,
Tomas