It depends to what do you want to input it to? If you want to use it as an input for madmapper then you can just hit on output and select syphon, then madmapper will recognize it as an input trough syphon.
If you want your M8 output to be recognize as a usb camera input, you can use an application from
http://b-l-a-c-k-o-p.com/ called grabber window
http://b-l-a-c-k-o-p.com/GrabberWindow.html where it lets you select a window and use it as a video input on your own computer for stuff like Skype, G+ Hangouts, Facebookvideo, Chatroulette (these are the ones that I have tested but im sure it works in much more web pages that use video input) if you use the free version you will have a watermark on your final video, if you pay the license then the watermark is gone, this process I discovered after reading this thread
viewtopic.php?f=4&t=3671 the way I explained it to you its a bit different from the one in that post because the new versions of M8 accept video input from webcams, and I am using grabberwindow instead of grabberraster because it works better when using spaces and totally forget camcamx there is no need for this virtual mixer you can just do it directly from M8
I dont know if those are the kind of things you want to input your M8's output but those are the ones I have used, I think you can also output it to a video mixer like an edirol V4 but im not sure I've never used them before
hope this was helpfull, if not tell us what do you want to input it to?