The issue is mono sound from the rear panel audio output. The front panel headphone audio & HDMI audio is OK (stereo). OEM integrated sound, stereo only on this model, no surround sound.
Easy to test this with speaker configuration test in plackback devices/configure/speaker setup, or from the DTS control panel. Tone at left speaker, delay, tone at right speaker, is normal.
Issue is, running speaker configuration tone is heard from both left and right speakers at the same time,
when each tone should be from only one speaker at a time. Volume is also quieter than normal configuration test.
New, out of the box it worked. After 2 days Windows 10 Home completed the update to the new build (1511).
After the update I was familiarizing myself with the audio settings and noticed the issue.
I uninstalled the OEM audio driver and re-installed the version on the HP driver support site. (same version)
Shortly after that, a newer audio driver was available from HP Support assistant. I installed the latest audio driver.
The issue persisted.
June 9th I contacted HP phone support and after some discussion, eventually a supervisor zeroed some regisitry values that had values of 1 rather than 0 and that fixed it.
The registry values were in the area of, HKEY_Local_Machine>Software>SRS Labs>APO>and then within the next 6 lines of registry. He modified about 5 or 6 values to zero, rebooted, and the issue was fixed.
On June 15th there was a Windows cumulative update KB3163018 and another KB3149135.
The first attempt at the KB3163018 install failed, but on the second attempt it was sucessful.
I immediately tried the speaker configuration test after the Windows update and the issue with mono output from just the rear audio output returned. Seems to be caused by Windows, but the only Windows support for OEM Windows software is the desktop manufacturer, so I phoned HP again on June 17th.
Since this may be an ongoing issue, I was planning on archiving the registry changes this time, so I could modify the registry values myself if this issue was chronic. The HP rep. didn't acknowledge my asking him to slowly make the registry changes so that I could write them down. He quickly zeroed only 3 or 4 values and then had me check the results. The issue was not fixed this time. He stated that he changed all of the registry values required.
I told him the other rep had changed more values and had me restart the PC before checking if the issue was fixed. Tried the restart, no luck.
He then suggested uninstalling and re-installing the audio driver. I told him that I had previously done that twice without it fixing the issue.
Then he suggested a system restore to an earlier date or a system recovery.
Now, those two options would probably fix the issue, but I would be right back in the same boat after the same Windows updates that would be in line to be installed.
So the issue remains unresolved.
I would be interested in knowing the registry values that the first HP rep. zeroed so I could check the values myself.