AMD Support took my info, but haven't responded yet. I took some advice from members of the Anandtech forum, and got a new motherboard.
Goodbye, HP......welcome, Gigabyte.
I installed a new motherboard this morning (Gigabyte H77M-D3H, ~$95 at Fry's), and everything's working well now. The installation was fairly easy (about 90 minutes); here are the only non-plug-and-play portions of the process:
1. Verified front panel power switch/indicator header with multimeter (continuity and diode test). HP/Pegatron did not provide a pinout for the header.
2. Peeled heat sink solder-side bracket off of old mother board. The solder-side insulator is half as thick now, as it de-laminated and left half of its thickness on the old board. I didn't sweat it; the voltages are way too low to pose a dielectric withstand problem.
3. Activated Intel RSD, RAID mode, and the Ethernet adapter in the BIOS (all toggles).
4. Note: the DVI-D cable didn't achieve native resolution on my 21:9 Dell U2913WM monitor. It interpolated it in 4:3 aspect ratio. When I switched to DisplayPort/Mini DisplayPort, it was correct.
It was, to date, the most painless motherboard install I've had to do, though it should be noted that I've bought pre-configured systems from Dell, Lenovo and HP for the last 10 years.
Bottom line: here are the comparative PassMark numbers.
Old HPE-510t (with Quadro 600 and SSD upgrade):
Upgraded with Gigabyte H77M-D3H and AMD FirePro W5000:
2D performance is slightly decreased (I noticed it in Altium Designer...Quadro drivers more optimal?), but not significantly. 3D is much better.