Wow, audio hardware like that is way outside of anything I've worked with before.
So my curiosity peaked, I've done a bit more research. Take my findings with a grain of salt, as this is not my area of study and I could be completely wrong.
As mentioned in that
youtube video, the unpopulated resistor pads correspond to the PCIe pin labeled
CLKREQ#. This connection is responsible for enabling the
bus reference clock. The primary reason for this pin is
power savings, since it disables the chip responsible for adjusting the PCIe bus speed.
So, here is my theory. The
network card needed to instruct the motherboard to use an
optimal clock speed. However, it couldn't do so without the reference clock pin. For your device, the default bus speed must already be what the sound card expects. This make some sense since the
MOTU 424 was originally manufactured as PCI/PCI--X , with far less bandwidth that PCIe x1.
Effectively this plug and play result will not be the same for everyone, as it depends on the attached device and what PCIe standards it requires. I've included a number of embedded links to go with my findings but again, I'm not an expert by any means.
