I would still suggest not to do cardio afterward. Even if HIIT has been shown to be muscle sparing I would be concerned with where the nutrients are going. If i just finished up with a heavy chest day, I want every bit of protein and carbohydrates i'm ingesting during and immediately after going to rebuild my pecs. I don't want it being used to fuel my cardio session. HIIT, due to its higher intensity is more likely to burn through glycogen, when you take in carbs and protein post workout it will go to refill the glycogen you just used up. Again, I want every bit of nutrients going to rebuild my pecs after my chest days.