Not sure if the 748R airbox will fit, or if it is just just for 'Kyalami' frames?
Anyway you can get a larger airbox from EVR
EVR Edo Vigna Racing it's claimed to be double the volume and the bike will breath better with it.
I have one on my 916 and it works very well.
I don't know about shower injectors but wouldn't think they'd be worth much without extensive tuning?
Here's a pic of EVR airbox next to a stock airbox;