You can upgrade your turbo with stock injectors if you like?
Some BT tuners will change injectors for safety, some dont.
One firm quotes near 350hp on stock injectors.
I would suggest you contact the tuning companies to ask their advice prices and specs. You do not mention what upgrade you are looking for, ie if you want mega power, like 400-500hp, or if 330 odd will do.
For big power you need big injectors....and roda, pistones, valves etc! Its mega bucks, but you can get a quoted c.350hp , for £4k all in, on stock injectors...!