[LDS]

I'm not sure your problem has been communicated very well. Just to be clear - you are running Avid HDX hardware with Pro Tools, but all of your Windows 10 audio (playing a file from the audio file folder, soundminer and RX) is routed to your Blackmagic interface. Correct?

And you can record and playback audio just fine within Pro Tools? So Pro Tools and your HDX card is working just fine?

But when you try and play back audio through Windows 10, which is set to your Blackmagic card, such as straight from the audio files folder of a Pro Tools session, or from Soundminer, or from RX, you have sound quality issues?

That points to your Blackmagic card being the problem. Have you tried plugging the Blackmagic card straight into your monitors to determine if it is working ok? Have you tried selecting your Avid HDX hardware for Windows 10 audio, which bypasses the Blackmagic altogether, to see if the problems suddenly disappear?

Have you tried any troubleshooting steps to narrow down the issue? If the Blackmagic interface and HDX aren't playing well together, try and figure out if they are playing well when separated.

On a side note, the way you currently having the Blackmagic card feeding HDX via analogue means you are probably actually losing sound quality. You really should consider doing it digitally (AES, optical spdif, etc) instead, as well as jamming the Blackmagic to HDX's word clock.