While Greenhorn's response may appear to be lateral thinking, he has made an Important point.,
I believe that most beginner's setups lack treble not because of poor performance of the Amp and / or speakers, but because of poor source material.
What are you using for your source ? A DAC + Music files ? Try listening to a few better quality music files or better source hardware (ie DAC or CD Player) and you will be pleasantly surprised.
Another tip, position your speakers so that the Tweeters are directed at your ears when you are properly seated at the listening position.