Hello Jason
Axis actually has something that allows you to make viewer as you describe:
AXIS Media Control ActiveX component enables easy viewing of Motion JPEG, MPEG-4* and H.264* streams directly in Microsoft Internet Explorer and other ActiveX containers.
http://www.axis.com/global/en/support/developer-support/windows-development
It is really very simple to make a Windows desktop application to display a number of Axis cameras in a grids-style fashion. You mention 6 cameras, but is easier to make something to display 4 camera (2 x 2) or 9 cameras (3 x 3) as you can device a FullHD 1920 x 1080 monitor into multiple windows with the same aspect ratio (16:9) If you display just 6 cameras, in the correct aspect ratio, you'll have a lot of unused pixels on your monitor (black bars)
I guess everyone in the CCTV world knows VLC Player.
Note that VLC https://www.videolan.org/ offers a similar ActiveX component that makes it easy to make small Windows desktops applications that display generic RTSP stream. The Axis cameras will also work with this.
You can use the mentioned ActiveX components in Microsoft Visual Studio, of which free versions are available: https://www.visualstudio.com/vs-2015-product-editions
Hope this helps,