my own speaker is ruler flat(plus/or minus 1.5 db)to 25khz
If you're -3db @ 20-25kHz the only reason to boost your hi freq is if the room is damped: the wavelength at 20kHz is very short, so average thickness material will absorb...
Assuming you want a HF spl boost, use a 1st order & cut higher rather than lower. The good thing is that the s-tweet's upper resonance will be too high (~100Khz) to be significant in the audible spectrum as its effects daisy-chain downward.
But there, you'll need a Murata or a Tad (or Townshend/Tannoy -- but they're very expensive). There is also a FOuntek s-tweet that's priced logically. The Fountek mentioned above is a normal tweet (37kHz) and will only boost your audible hi-frequencies.
Measure yr main spkrs' power rating & make sure you equalise the s-tweet accordingly. Also make sure you place it correctly on the same vertical acoustic plane as the tweet while you're at it -- or you'll be out of phase with the tweet!
Cheers