hi,
sorry ive never had any experience with the mods you describe although i bet it does make it go fast afterwards!
however as a volvo tech you should be aware that ANY mods to your xc90 such as you describe will completely invalidate the warrenty on the whole vehicle, as the ecu would be reprogrammed with aftermarket software this then affects the whole communication network that runs the xc90s electrical system and therefore volvo can argue that this mod could cause problems in other areas of the cars system. check volvos website if you dont believe me but i know for a fact this is true your warrenty would be worthless and trust me you will need it...
even once the cars out of warrenty aftermarket software could cause future problems and can corrupt volvos software database if you need updates in the future.
the mod you metion about the boost increase can be risky for the transmission also especially on the t6 with auto box,it doesnt handle big power very well.
i dont mean to put a damper on anything but as a tech i see the value of warrenty that a new car provides and i would hate to see you invalidate yours.

steve.