If you have an amp, try the cheapest alternative first, go with the passive filters and just pick the one you want to Xover at. The Harrison knock offs didn't cost that much if I recall. But, if you are wanting to go plate amp, then the ones from parts express are the same ones used in many speaker systems, they just OEM them direct to help the DIY crowd. Sometimes they have them on sale and you can get a good deal of power for the $$'s you spend. I recommend partsexpress because I have been using them for 10+ years and they have always taken good care of me.