Make your resolution as high as it will go on your monitor, and open multiple windows of IE to view the cameras online with the factory ActiveX website. Maybe 3x2 grid of Ie windows, each showing 8 channels.
Other option for viewing live video would be to use Blue Iris, as this is the only PC software I've used that will access analog Zmodo DVR's streams over the network/internet. Similar to IPCam VIewer on android/iphone. This way you could have one desktop window (Blue Iris), with a large grid of the cameras. Obviously resolution will suffer but it will work.
This is all assuming you're using analog DVRs. I know nothing about Zmodo NVRs and how you access those streams.