Get an amp with a tube preamp but do not crank the gain. But of course if the gain is to low it won't work. The way i set the gain on atube preamp is listen for the whoosh and backoff, you need to listen close to the speaker at first Then plug in the bass and backoff some if the loudest notes break.
That lowish gain range will naturally give sparkle. This is how many guitar tube amps operate. They go darker as you saturate the gain., specially if they have passive tone stack For solid state amp, and specially if they offer boost cut just look at the specs and although it is counter intuitive, the lower the frequency where the high shelf starts, the brighter it will sound up to a point. IME 6-7Khz will be noticeably be brighter than one at 10KHz. Because we are not dogs , so when the shelf is higher the effect is less. James/Baxandall tone stacks seem to be brighter as well.
The more hi-fi the amp, my experience is that it will not be overly bright in the neutral positions but may have enough boost to get your there. AI amps behave like this.
Also voicing controls help, but IMO tube preamps at lower gain seem to bring out the highs in a natural way. Any of aged horses deigns with a tube preamp with Genz Benz, Genzler and Mesa will be my recommendation. GK, Trickfish and Even an SVT can be bright if you are using a Hifi cab like an Berg.
Edit: So I borrowed my friend's fusion-S and that is definitely a brighter amp - I recorded my noodling. According to GK the high shelf +/-14dB @ 7KHz, compared to the compound shelf in the Streamliner +8/-12dB of effective cut/boost at 4K Hz and approximately +/- 12 db at 12.5K Hz (which is not easy to hear ) The GK even gets brighter due to the Contour +2dB @ 50Hz/ -10dB @ 500Hz/ +3dB @ 7 KHz. when I had the 150MB combo, I always had that on and I think many GK users do.
About the streamliner not sure what the slope on that lower treble , but it is useful but also a little quirky which makes it a very interesting amp. The EQ is using the tubes, 1 tube for the bass and treble and the other tube for the mid and the first one for the gain stages. Not sure how the GK Fusion tube use is. No block diagram in the manual. I would imagine it is similar because they also use 3 tubes.