I needed to use the HDMI and AV cables simultaneously. This was due to my 20″ PC monitor not having built-in speakers. I use a DVI to HDMI cable, DVI connected to the monitor and HDMI into the Xbox 360. This works fine except I have no sound. This is why I need to use the AV connector so I can route the sound to my stereo.
Below is the standard Xbox 360 AV connector.
All you need to do is separate the casing. Use something sharp and rigid, using a prying motion.
Now I can fit both the AV and HDMI connectors into the 360.
I suggest inserting the AV cable first, then the HDMI. It’s a tight squeeze but it works.