Have you tried using the tuner in the 990? If it works, you can eliminate the downsteam components and focus on 990 and upstream cables. If it doesn't you can try driving the ATI from some other source (e.g. a laptop or Ipod) to verify that the downstream components from the 990 are working properly. You could also try connecting self powered speakers to the 990 (Gonk's recommendation) to test that the 990 is outputting a valid signal.