They do different things. Expansion chambers are meant to expand CO2 while it is entering the gun and regulators regulate the air while it is coming into the gun and keep it consistent which would help with keeping your velocity/accuracy consistent.
I'd just stick with an expansion chamber since you obviously use CO2 and A-5's are not needed to be regulated because if they were, they would come standard with their own regs. Plus CO2 doesn't work too well with most aftermarket regulators.
what's a good x to get? I really don't like the look of them cause (go ahead and yell at me now) I have a mil sim. Trinity makes an ak-47 clip x-chamber, but it is really long. I'd like something with a flat black look rather than gloss.
__________________
A-5
Flatline
E-Grip
Car Stock Skill
ACI x chambers are supposedly really good...i don't see why the regular tippmann one wouldn't work, though...
__________________
Tippmann 98 custom
-12" CP classic one piece barrel
-Double Trigger
-Tippmann drop forward
-Cyclone feed system
-68/4500 Pure Energy HPA tank