THX not a gimmick
Youv'e got to seperate out what THX is intended to do vs what you want to listen to.
THX is intended to make sure that what you hear at home relates in a meaningful way to what you would hear at the theater. It is a set of specs designed to make sure that your home equipment can handle the dynamics of oh, let's say, Star Wars. It deals with such things as dynamic range, correlation of surround, placement and type (monopole/dipole) of speakers etc. It says nothing about what makes a speaker sound good or bad.
dts on the other hand is an encoding scheme only comparable to Dolby Digital. THX supports both Dolby and dts. They are similar to whether you listen to a WAV file or an MP3 on your computer. Says nothing about your sound card or computer speakers.
Lets look at what makes a movie sound good compared to what makes music good.
When watching a movie the things that are important are:
Dialog is clear and understandable.
LFE effects rattle your chair
Surround effects effectively draw you into the scene. (flyovers, rainstorms)
Transition from soft dialog to bombs going off is undistorted.
When listening to music the important items are:
Flat response (20-20K) with minimal coloration so you hear exactly what was recorded.
Imaging to give a good "soundstage".
Dynamic range soft to bombs going off without distortion.
If you compare these two it becomes apparent that the center speaker, surrounds and sub are the important movie speakers while the L/R speakers and to a lesser extent the sub are the important music speakers. Both require excelent dynamic range. Both require broad response.
It seems obvious that a system that's good for music and that has matching capabilities in the center and surround speakers will work equally well for movies with one exception. A flat low end response will possibly be less than required to "rattle your chair". Many subs have a switch to correct this.
The reverse is not always true. A system can be fine for movies but totally inadequate in it's imaging and response curve for music.
So, THX is fine for what it's designed to do. It even helps with non THX gear as manufacturers try to meet most THX specs even if they don't want to pay for certification.
What THX won't do is determine if a system is good for music or if you like what it sounds like. For that you have to listen for yourself.
