i don't think you need a DSP kit as the DSP kit was for BMWs pre-03. it all depends on how the DSP is handled on your '06.

its VERY easy to add a DSP kit. if you can install a phatbox without a DSP kit, you can do one with.

no familiarity with X3, but in '03 and later X5, the DSP kit is not needed. the clincher is that my sister's 04 Z4 DOES need a DSP kit for the PB.

you run a 50/50 chance of requiring it. very easy to do, either way.

-d