Hi Tony, As you probably know, the front two speakers are the tweeters and of course only handle the higher frequencies, which tend to have less sound energy than the mid/bass frequencies. I tried the check that you did, using the 'DEMO' and it is difficult to tell if anything is coming out of the tweeters. However if you put a reasonably thick book, say the KN7000 user manual, completely over the mid range speaker, it is quite evident that there is sound emanating from the tweeters. Hope this is the case with you and that they are not faulty.
After silence, that which comes nearest to expressing the inexpressible is Music.
( especially when the music is played on a KN7000....)