When it comes to getting visibility on your LAN you have two options. One is to download and install nProbe and set up a SPAN port off your 3560 core switch. If you are not familiar with setting up SPAN ports, we have developed a free tool which is available at this link for the purpose.
The other option would be to again setup a SPAN port and use a system like LANGuardian to do the analysis. LANGuardian uses deep packet analysis so you get more information from the packets like file and website names. It integrates with Orion products so you can view the data through your existing views.
Hope this helps,
For your "Unknown' nodes that you are trying to manage with WMI credentials, there is a WMI troubleshooting guide located at http://www.solarwinds.com/support/apm/docs/APMWMITroubleshooting.pdf. Basically, you will want to run wbemtest.exe first from the target server to verify local connectivity, and then from the Orion server to test network connectivity.