Stand Alone Super Tweeter for Revel F208?

Triangle would be one of the candidates, but other instruments have even more energy above 20KHz -- this is a very interesting article on the subject
https://www.cco.caltech.edu/~boyk/spectra/spectra.htm

Townshend is a good choice, as is the Enigmacoustics Sopranino

I do however have to note that a super tweeter should not add "sparkle" to your speaker. If you can hear the effect of a ST as sparkle you probably have the cross over set too low or the ST level set too high. The ST should be heard more as a tightening of transients and a greater appreciation for the space in the recording. You shouldn’t actually be hearing the ST (unless you are a dog or a teenager)

@honashagen have you considered that the room may be the issue? Treating the room with for example a set of SR HFTs may give you not only control of the room but also an ability to tune the high frequencies to suit your taste. For example in my room adding or removing one HFT at ear level front and center has a major impact on specificity and level of high frequencies (this is even true for removing one ball on the Vibratron but the SR ART system is much more expensive)

My point is that you need to consider how the speakers and room interact and by adjustng this may be able to tailor the sound to suit your preferences

Yes, the HFTs work -- the SR room treatments are a very effective way of dealing with even an under-treated room but they can also be used to optimize and fine tune a well treated room (like my setup)

They're cheap (or you can even DIY, search the 'Gon) and available on 30 day money back

@honashagen -- congratulations, the result you have achieved is exactly what I would have expected -- do you also find that the quality of the bass has improved, with more crispness and tightness to notes? Anyway having lived with STs for over a year now every time I would no be going back