Taking the foam sheet out can help with detail.
Just installed this exact system twice this week, but with Morel Dotechs instead of Virtus (from the last batch they had). No hiss.
The iPod into the amp(s) sounds fine, so it's not the Virtus tweeter or crossover set up wrong.
Any difference from different sources?
musicar northwest portland or musicarnw.com
Web site migration complete, still repairing problems. Sorry!