On renntech someone put in the 3.4 engine on the standard tiptronic, no issues there. I'm still researching it myself but what I hear is that the 3.4 engine and the tip from the 2.5/2.7 go together fine. The final gearing is maybe a bit short for the 3.4 but that seems no worry.
http://www.renntech.org/forums/index.php?showtopic=16061
Henk