I'm looking at floor speakers and satellite speakers right now, I assume it's necessary to have the satellite speakers at the same impedance as the floor speakers in front? Is it a bad idea not to buy a fully matched floor/satellite set?
Why floor speakers particularly? Front three are the most important to match, but I do also like to have a full surround set at least of same model/line from a brand speakers. As far as impedance you just want to make sure the amp/avr can drive them well, avrs are often not a good match for very low impedance (4 and below) speakers, especially the lower end models where they've not used the most robust power supplies; you don't have to have them all with the same nominal impedance rating, tho. Active speakers would generally have sufficient amps designed for their use, tho. Keep in mind an impedance rating for a passive speaker is a nominal rating, but the impedance will vary with frequency, and phase angle can come into play to put more strain on the amp as well, especially if you want to play at high volume levels.
HTD speakers I've seen good comments on but no personal experience. Lots of us that buy and like our speakers will recommend them
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For example, I've had good experience with Ascend Acoustics, would and do recommend them. Philharmonic Audio's Affordable Accuracy speakers are also very good (and I've built the kit they're based on, the Dayton BR-1 kit available at parts-express.com), and will build another with the same crossovers forum member Dennis Murphy, who is Philharmonic Audio. Excellent value. Many others out there as well.
Biggest question is what's your budget? What are you aiming at in terms of speakers/subs? What size room are they going to be moved into? Suggest you line up some more info along the lines of my questions and start a new thread with an appropriate title rather than this one....and read some more threads, lots around that will cover some of the questions/angles....