I've got a s1600 which is the same as a metal (except the colour scheme). They do sound lovely for a standard car. I see where you're coming from.
If you were to get a mountune on a zetec S it would make it the same bhp as a metal/s1600 and you'd get the twin exhausts. But you'd also get a spoiler extension.
As for the front bumper I'm sure the ZS has a splitter lip
Any how welcome to the forum! Upload some pics when you get it
Thats what i thought about the bumper i was sure the zetec S had it but one of the sales men was more than adamant that they didn't, as for the spoiler you still have to buy it extra if you buy the kit from mountune, It doesn't come in the kit as standard