I don't have Win 8.1 but I updated my drivers last night. I have to say that Sonar loads faster now. It used to give the (not responding) in the title bar all the time with the old drivers. I can't say it still doesn't do that all the time anymore and still loads faster. It was weird when I got the (not responding) before because it always started after a bit anyway.
 
Has anyone tried the new drivers with 8.1?

Very, cool.  I have also been experiencing very long load time, that I have attributed to the octa-captures drivers.  I will have to try and update to 1.52 as well.  What version of windows are you using.  I am currently on windows 7.

will those drivers make the studio capture start sooner too?

Yes, last Saturday I downloaded the 1.5.2 drivers. The earlier drivers do not work with windows 8.1, but 1.5.2 does so!
1.5.2 is only an update for drivers, not for the system.
So you must use the 1.5.2 drivers and 1.5.1 system software with windows 8.1

1.52 drivers seem to work rather well so far in 8.1.

I tired the 1.52 driver for QuadCapture with Windows 7 x64 and after re-tweaking my settings in Sonar (uninstalling the previous version seems to have blown out all my previous settings) it did seem that I had a little more overhead and that things ran smoother.
 
Maybe its just a placebo affect.
Anyway - the point is that 1.52 did seem to help even in Window 7 but to notate your Sonar driver settings before proceeding.

Just in reading the instructions to update both the system software to 1.51 and the audio driver to 1.52 it says to uninstall everything first, unplug everything etc.  Did you guys do this? I don't remember uninstalling last time.  

sven450
Just in reading the instructions to update both the system software to 1.51 and the audio driver to 1.52 it says to uninstall everything first, unplug everything etc.  Did you guys do this? I don't remember uninstalling last time.  

Both this version and the previous gave me a warning when I tried to update without uninstalling the previous versions.
Suspect that's why the settings for my previous version evaporated.

Yep uninstall old driver version first. I also did that last time. I'm sure that was by Roland's instruction.

I never had a problem with settings. I was surprised that my control panel in the taskbar stayed there. I forgot to check the preferences in Sonar but I'll give it a look.