I'll chime in even though I'm talking out of my ass.... I think finding a perfect match for using X3 or X5's in a HT will be difficult unless you have a big room or acoustically transparent screen that can accomodate an OB speaker as a center channel and as surrounds. I'm assuming you don't have such a space. If you do, bless you and ignore everything I'll say and just see if you can buy 5 X-series speakers and you're good to go. However, if you don't have such a space I would just focus on finding a center and surrounds that sound "similar". I've used mismatched speakers in my "theater room" for years, even matching a different center channel from the front mains, and for home theater I don't think it makes a huge difference. When I say "similar" I mean that I would try and find a speaker with similar dynamics, similar tweeter type, and similar efficiencies so that they present the amp a similar load. If you have a processor with room correction it will help balance different speakers somewhat so that should help. So, for these speakers I would try and find something with a ribbon style tweeter that is fairly efficient. I think a good budget match may be the Emotiva C2, if you can find one. It's a big center with an AMT tweeter. It isn't nearly as high fidelity as the X-series Spatials, but for movies and tv its pretty good. Another option is to just forget the center and use a phantom center. The imaging of the Spatials is good enough to create a center image and the money not spent could be used for better subs. Or, you can contact someone like Selah audio to possible make something custom that they think would match. For surrounds I tend to not spend a lot. I'd look at the Emotiva surrounds which again use an AMT tweeter. Another option is something like PSA Audio speakers, which could also maybe work for the center channel. Those are high efficiency and dynamic. For subs, I'd look for something fast. To me the best out there are Rythmiks. Take your pick. If Spatial creates a sub that would obviously be an option as well. Anyway, just my thoughts for what they're worth.