I seem to remember that it's not possible to remove an injector without removing the manifold as they sit right in the middle of it all (Poor explanation but if you look at the position of them you'll see what I mean).

To give you a bit more explanation as to the reasoning for my suggestion...

We had a 52 plate A2 BAD with exactly the same problem. The car ran fine, no obvious misfire but had the fault codes for a misfire. Incidently it had a very slight rough idle but I think they're not as perfect as some other engines anyway. It came to us already having 2 new coils fitted elsewhere. We replaced these with a new genuine set so we knew where we were at. Same as you I checked the wiring as they suffer with this, plugs, compression etc etc. Anyway, we suggested the customer take it to Audi for their opinion and they said the head needed to come off as the compression was low (even though we had already tested and found it to be fine). At the customer's request I pulled the head off and did the usual. Put it back together and it was still the same. Fault was finally fixed when someone who had seen this before suggested the MAF. Just a shame the customer had to go through all that pain to get there.

My feeling is that it's much easier to change an airflow meter than an injector. Not a pleasent job.

Good luck!