You will have to calculate how much the extra boost will decrease the fuel pressure, and size the injectors accordingly.

For example, if the stock injectors are 270cc, and run at 45psi, with 10psi of boost you only have 35psi.

If the boost is increased to 20psi, then you only have 25psi at the injector, so the injector will need to be sized 18% larger to compensate.

Then of course, the chip will probably need to be changed too...

If you already have a chip that compensates for the extra boost, then normal injector math should apply.

and I wonder if this unit would to the trick of tuning with stock software? or would there still be a bunch of other variables?<ul><li><a href="http://216.242.145.16/products/product.phtml?p=32">Aeromotive digtal fmu</a></li></ul>

Adjust % = square root (new fuel pressure / old fuel pressure)

The aeromotive unit looks like it needs an external pump to provide the pressure increase.

I'd really be interested to see how the returnless system works on the B6. If it's controlled by the ECU, you could use something like this:
<a href="http://www.mafterburner.com/afterburner-efpc.htm" target="_blank">Afterburner</a>

I'd have to see a wiring schematic to know for sure though.

so its square root of (25/35)? i end up with 85% and 100 - 85% = 15% ?

Although soon, I'm hoping to get rid of having to used add-on boxes. I'm working on it :)

Depends on how you look at the equation:
sq rt(35/25) = 1.18 =&gt; 18%

The injectors at 35psi will flow 18% more than injectors at 25psi, so you need 18% larger injectors.