Those HP monitors are meant to be used as your computer monitor. They only support computer based RGB 444 signals via DisplayPort and DVI-D and does not support embedded audio.
The UltraStudio Mini Monitor only outputs YUV 422 at a maximum of 1080i59.94 or 1080p30. It also embeds the audio into the video signal and can't keep the audio in sync if you try to split the audio out of your sound card instead. It is far cheaper to just use the Dreamcolor monitor directly as one of your computer monitors, and avoid the audio sync issues at the same time.