The firmware issue was a leading symptom to a general problem with a Dell Precision T1650.
Starting the HDSP-Mixer caused severe stuttering of mouse pointer movement and input lags until the machine hung.
I had to power off the pc by holding the power switch.
Same with all applications calling the HDSP driver.
The issue could be reproduced with fully patched Windows 7 32 bit and 64 bit.
It could not be reproduced on a Dell Optiplex 790.
Configuration:
HDSPe MADI:
Firmware Version 29
Hardware Rev. 1.1
Driver 3.35
Dell Precision T1650 (BIOS A12):
CPU - Xeon E3-1240
Chipset - C216
RAM - 2x4GB
VGA - Nvidia Quadro 600
Solution:
Put the HDSPe MADI into the first PCIe slot,
which is normally occupied by the VGA.
The VGA Quadro 600 is now plugged into the 2nd PCIe slot.
All energy/power saving options in OS or BIOS were left default.