I've had to temporarily set up my exhaust without the split air pipe on my S5. It broke off the cat so I welded the cat hole up to plug the massive leak, but I'm wondering now if I need the pressure from the split air pipe to help open the 5th and 6th ports.

 

Nope.
S4's do though.

 

You don't need the split air to operate the 5th / 6th port actuators, but you probably will need it to pass your next CA emissions test - both the visual exam and the tailpipe sniff. Good luck!

 

I just did about a week ago.
Funny to think that I've read so many posts about "melting" cats because "the split air system cools them down"
In fact it's the opposite. The system supplies oxygen to feed your exhaust flames and help burn off all the extra crap. Your exhaust is actually cooler without it.

 

If you get caught tampering with emissions devices in CA, you can get fined up to $2,500 for each part that you modified or removed, as well as jail time. You had better hope like hell that you don't ever get stopped by a police officer or get involved in a collision.
http://www.arb.ca.gov/msprog/aftermk...tallcatq&a.pdf

No, the split air pipe supplies oxygen that is needed for the 3-way cat to perform an efficient chemical reaction to control NOx. It is a catalyst, not an afterburner, lol.

If fuel is burning in your cat, then something is very wrong with the mixture because the engine is running too rich and there may also be an exhaust leak. Yes, this will melt your cat because cats are not designed for combustion.