I've been doing some research but can't really find the answers I need ....

I'm looking at capturing 3-6 video sources directly into my iMac simultaneously for use with a software vision mixer solution (something lie BoinxTV). The iMac has 2 thunderbolt and 4 USB3 ports, so individually those ports have enough r/w speed.

But 2 things worry me, capturing multiple streams at once and overloading the bus that deals with those ports.
And also is it as simple as using the camera's video out into the USB / TB ports and the software will recognise them as video streams.

Otherwise I guess I'll have to look at hardware vision mixers.

Cheers in advance

Nick