The first thing is to do one camera at a time and watch what happens in BI5 and watch the cpu loading.How did you get it to work? I went from 8 1080P cameras with CPU at 30%; after enabling sub streams my CPU jumped over 80%.
What resolution did you set the sub streams to in the actual camera web server settings (Not the BI5 camera settings) ? What we are doing here is giving BI5 a much lower resolution image to do motion detection on, so it makes sense that the cpu load for motion detection is reduced; the main stream should be direct to disk for H264.
For example, looking at the actual camera web server page, the main stream for my Dahua camera is 1920x1080, and the sub stream is 704x576(D1). When I look at the BI5 settings for this camera, in the General tab, I can see:
Main stream 2.1MP, 11.99/1.00 fps, 263.3 kB/s.
Sub stream 0.4MP, 11.00/1.00 fps, 64.4 kB/s.
So even though I have increased the overall network traffic, BI5 can do motion detection on a 0.4MP image instead of the 2.1MP image. My cpu loading went down from around 18% to 8% by doing this to three cameras.
Historically, the internet was full of people asking"Why does Blue iris use so much cpu ?". The answer was that other software was doing motion detection on the sub streams.