Welcome to the forum.
Like you, when I first got my zed I fitted Berk HFC, cobra Y-pipe and a japspeed k1. Sounds brilliant!
From what I've heard, The best air filter is the standard airbox ('06) with a high flow panel filter.
I was also looking at the kinetix plenums, although the look the nuts, they will loose power. They have been proven on dyno to be @*!#. Best of just getting a plenum spacer.