Unless the two halves of the one of the preamp tubes are drastically mismatched,you wont notice any difference using the "matched" triode in the PI position.Matched triodes are more relevant in HI-FI use when everything is aimed at zero distortion.As you have already pointed out you cant hear a difference when switching the tubes around,so dont sweat which one is matched or balanced.In my experience and my opinion is that balanced PI tubes are a lot of hype,the 2 sides of your output tranny arent matched so the PI tube aint gonna make that much difference,and most matched power tubes are likely off by as much as 5ma's anyway.
