I currently have polk tsi 500's and I want to upgrade them into something that would produce a better sound for movies and music. I have a Harmon 3550HD and polks for the center and rear. Would you get the Rtia 9 or the def tech 7004.
They are both different sounding speakers. The Def Techs are bipolar and the polks are direct. For music I would go polk but for movies I would go def tech.
I suggest checking out the Mythos line from Def tech if music is important in your system. Personally I don't like bi polar speakers for music but thats just me. The Mythos 1's would be a good speaker to put in your mix. I think that maybe the right choice.
Also be advised (you may know this already) that if you go with the Def-Techs they like to have some "Breathing room" between themselves and the wall behind them. There are countless posts here and other forums about this fact. It will make a tremendous difference in the way that they sound. So look at the depth of the speaker and where you are wanting to place them. I would say a bare minimum of 8 inches away from the wall. There are many that have them 12-14" away due to the fact that their setup's allow this. This will dramatically effect the sound stage.
Both are good speakers. Mantis states that he does not like bi-polar speakers for music and I do, so there are plenty in both camps, just know that the placement will be more critical with the Def-Techs.
Good luck and enjoy which ever you choose as I do not feel that there is a "wrong" choice to be made here. Just make sure you take music/movies you know well and demo both A LOT and see which one you ultimately just like better.