Welcome to AudioCircle!
Did you blow the tweeters by playing them too loud?
Seriously, put your ear against the tweeters while playing cymbals at very low volume and listen for any sound coming from them.
Try some other electronics, if available. Check if any EQ is applied in the electronics, like player software, tone control, room correction recalibrate, weird or broken cables, very plush room decor, or stuffed chairs next to the speakers. Make sure the speaker cable connections are clean and tight on both ends because electrical damping affects treble as well as bass.
Although the high frequency resolution on Debut may be less than audiophile tweeters would provide, Debut should still have relatively flat frequency response to 20kHz. Meaning the highs should still be loud enough even if not as detailed. So by "dull" do you mean that resolution (tonal and transient detail) is lacking? (cheap)
Or is the treble actually playing too soft in comparison to the midrange frequencies? (broken)
If everything is healthy and you want more resolution, my personal advice is you're ready to upgrade to your next speakers. Modding rarely works out as well as expected. Modding is a hobby in itself. Fun if you like messing with things. Not fun if you just want to listen to music and not technically inclined and just doing it to save money. In the long term modding and DIY cost more than upgrading.
But if you just can't help yourself
upgrading the stock tweeter resistors to Mills wirewound 5W, with the same values as stock will add some resolution without changing SPL. The added resolution actually sounds like added SPL, so it might be good both ways without needing to measure, etc. They are $7ea partsexpress, you'll probably need 4 total. Start a thread in Enclosures Circle or The Lab if you need help/advice with mods.
