Things are getting even weirder.

Now that I disabled more services that are not needed and fiddled with the nVidia settings (and then set it back to what it was before) I get audible USB noise in my OctaCapture direct monitoring i.e. I have some sort of a constant high freq hum and when I move windows around it changes and gets louder ... I'm sure that wasn't there 2 days ago ...

OK, the weird thing is solved.

That humming came from having cables plugged into the audio interface with a DI box at the other end, which was switched off since it was not in use.  With the DI on, the USB noisy interference when moving windows is gone ... strange, and beyond my current understanding of the world, but true ...

What still puzzles me is if this would also be the case if the USB cables are pluuged into a separate USB PCI interface and not the motherboard??? Any suggestions???

As regards the original NVIDIA problem: Despite trying all of most welcome suggestions, it's still the same. So I ordered an 5450 card which I will give a try in a few days.

FreeFlyBertl > the hum sounds like an oldschool ground loop, no?

FYI, the problem is solved!

ATI 5450 did the job. 32 EUR fix from amazon. installed w/ latest drivers, no fiddling about but all latency problems related to the graphic card driver interferring are gone (graphics stay way down in the latency ranking).

I wish I could mark this thread as solved, but can't find the knobs (using IE 9 64 bit).

I'm still a little disappointed that I can't go below ASIO setting 4 (96 samples ~ 12ms latency), but I reckon that Roland interfaces aren't stable enough at low buffers for extended periods (works for 2 mins, but eventually stops). Anyway, with all those routing options for direct monitoring on the Octa-Capture I don't really have to go that low ...

Just an hour ago I changed from my NVIDIA Geforce 7300 to a ATI 5450 and resolved another issue with WAVES Plugin GUIs (jerky parameter controls).


It seems ATI is the way to go for DAWS according to SOS.  Cool ;>

FreeFlyBertl

I'm still a little disappointed that I can't go below ASIO setting 4 (96 samples ~ 12ms latency), but I reckon that Roland interfaces aren't stable enough at low buffers for extended periods (works for 2 mins, but eventually stops). Anyway, with all those routing options for direct monitoring on the Octa-Capture I don't really have to go that low ...

I have to apologize and get something straight here: I forgot to change one important settings!
 
I'm using a VS-700 and a Octa-Capture synced via VS EXPAND; since it worked quite nicely with the Octa-Capture 1.51 drivers and my new DAW provides a lot of CPU power, it did work OK despite my inability to set the synchronisation in the VS-700 to DIGITAL 1 (which it has to be according to the manual).
 
Now that I'm using the correct sync mode these interfaces really ROCK!!! I can record at ASIO buffer sizes of 48 samples without drop outs or glitches for 10+ minutes!!
 

 

With the nVidea did you? a) Uninstall the drivers. b) Reboot c) Install the latest driver, ONLY install the driver, nothing else - no auto update or phyx/3D/HDMI drivers etc. Guess the point is moot now... Cheers... Alex

Tried loads of driver versions.  Uninstalled etc.

It´s maybe just another funny option. All the nVidia Problems shown by latMon (or other tools) are mostly based on OEM (build) cards like the 630 series (330,430,540, etc.). These cards are just labeled  to the 600 series. It´s not the GPU which is working on the upper 600er series cards. (or the OEM cards are build with defect GPU which are running while they just disable a core or whatever.) 
A friend of Me got the same problem...Beast of an machine, but a cheap graphic card build in... cubase 6.5 crackles.
A few years ago...we´d got an southbridge and northbridge chipset which managed a lot of things...now it´s all on the CPU. 

...Every PCgamer forum is "preaching" never build a machine where the graphic card is a bottleneck and can slowing the whole configuration. 

  Just try to invest in an better one...nVidia or ATI...but I think it´s logic: Building an "hell of a machine" by saving a few Euros/Dollars for the graphic card could´nt be the best option...