I don't think that Korallias (even the 4s) will give you the flow you want in a 125 6' tank. I've got a K4 and I can't feel it across my 120, which is 4'. I've got 2 seio 1100s, but I'm looking to upgrade in the near future, if I can ($$$).
Also with the Korallias and the red sea wave maker, you're going to get a lot of differing opinions on whether or not to do that. I believe Pedromatic has been running them for for a while on that wavemaker, but most peole would not suggest it. A better controller, though significantly more expensive, is the Seio controller, for Seio pumps, but it works on any of those type of powerheads.