First of all the results of LatencyMon are only an indication, XPerf is the only reliable and very comprehensive source for in-deep analysis. I'm thinking about putting together an easier to use XPerf package, but that may take some time.
DXGKRNL.SYS is a Windows graphic kernel driver. Have a look at the following thread that others are having similar problems with NVidia cards, too. I still suspect your graphic-card to be the culprit.
http://www.rme-audio.de/forum/viewtopic.php?id=9469
That running Cubase causes higher DPCs is likely connected to Cubases GUI drawing. So you may have to stay on the "Standard VGA driver" for audio work. You may try two things though: 1) Turn Aero off. 2) Download "PowerMizer Manager" and switch the graphic mode to medium or high performance 3D *permanently*.
AFD.SYS is a Windows network stack driver. Try disabling your network card to see if this lowers the DPC values.
NDIS.SYS is a mixed system driver, can be connected to network and graphics, but other stuff, too (printers). Again try disabling your network card.
IOSTOR.SYS is the Intel Matrix Storage device driver. You can try uninstalling it and have Windows use its own standard driver (which usually works with any non-raid HD controller anyway). That being said the "maximum" value listed doesn't tell much and I don't think that this is a culprit. The Acer laptop of my wife uses the same driver and has lower overall DPCs than my Macbook Pro.
ACPI.SYS this driver polls your battery status every 15 seconds and thus creates a DPC spike up to over 1000 us. You can disable it via Device-Manager -> ACPI compliant battery method.