How big is your room? Volume??? (LxWxH)
Unless you are trying to shake the foundations of heaven itself...
Your best bet is matching make and model. After that, you need to look for similar metrics in terms of frequency, roll off, spl, etc. The better matched, the easier it is, but at that point you probably also need to employ REW and a MiniDSPHD2x4 to help bring them together in a functional way. There are cats here that have mixed different brands, sizes, etc... but they all say it is a royal pain to integrate them well.