There are several leads available for the MMI in your Q5, you may have the wrong one. I would nip to your nearest Audi dealer and speak to the guys in the parts department. I find them very helpful and they sorted me with the right lead for my phone. I have 2 spare leads which came with my car (SQ5 - welcome to the Q5 club!), one has a maroon collar, part 4F0 051 510 R, and this is for ipod to mmi according to Amazon if you punch the reference into google. The other lead has a yellow collar (part 4F0 051 510 AL) also for ipod/iPhone with the small phone socket - if this makes sense!
You're welcome to PM with an offer if these are indeed the right ones for you. Hope this helps.
P.S have you joined the MYAUDIQ5 forum yet?