Do not worry much about the THX certification thing. Moreover a costly speaker does not necessarily mean that it would provide a better sound. Here is an excellent page
listing why, which and how to buy in ceiling speakers :
The main things
to consider while buying an in ceiling speaker are:
Go for wider range of frequency & with a smaller lower limit.
2) Power Handling(Watts)
: Get More Watt speaker for better sound especially if you have a large room. A more watt speaker will produce louder sound at a specified input than a lower watt speaker.
3) Sensitivity or Efficiency(dB)
: More dB means that the speaker can very effectively produce sounds without putting much strain on the amplifier. Go for more dB if you plan installing them for home theater setup.
there are some other things also like go for movable tweeters, timber match all the speakers
that you buy, must see the amp outputs to match with those of speakers
etc. I would highly recommend visiting the above page as it lists out all the things you need to consider before you buy an in ceiling speaker + also see the best in ceiling speakers you can buy at reasonable price.
Another thing, the in ceiling speakers may not suffice the bass you need(i.e low frequency outputs) so it is always better to invest in buying a subwoofer.
Personally I have got Klipsch In ceiling speakers R-1800-C
and a subwoofer. Thus it makes an excellent home theater setup
The R 1800 C have
1) 8" polymer cone woofer + a 1" polymer dome tweeter.
2) They have an incredibly good bass with frequency range 57hz to 20,000 Hz, 89dB sensitivity and peak power of 160 watts.
3) They are moisture resistant so install them in bathroom, patio, kitchen etc.
I hope this would help others as you might have already bought speakers.
Recommended Page: http://markmorgangenius.hubpages.com...d-Home-Theater