Tired of boring, polite, laid-back sound.....

Trying to hear "pulsating" from such a refined corner of the audio universe may not be possible when you compare to the brash upstarts here in the colonies (...er, United States).
At last year's Stereophile NYC spring audio show, Naim did provide energized, focused soundstage, along with sounds of real life, through their entry level electronics, and speakers, which might be in your stated budget. This year their website states their amps are "built to swing for another 25 years" so they seem compatible with your taste for action.
The NAIT 5i seems to be their current entry in the same range that impressed me at that show.

The "Brits" as you call them, are generally noted for their polite, laid back sound. If what you want is "lively, open, and energized", I suggest you consider something else (Adcom separates, Denon, Sony, or Onkyo receivers, Hafler separates, et. al.) See what some others might say. Good luck in your quest and happy listening.

I agree with Aball's and Listener57's choices. Naim and Triangle may be the most dynamic you can get at the $1K used level.

Besides Naim, Arcam could be your ticket. What is your planned budget again?

As an admittedly broad generalization, my experience is that a "lively, energized" sound is most reliably achieved in your price range using very efficient (93dB+ sens, MINIMUM impedance dip 6-7 ohms)loudspeakers with tube amplification of modest power (30-50W/ch). Omega Grande 6s powered by a 30W/ch 6L6GC-based amp cranks out beautiful, energetic music in my basement system at volumes that'll piss off even the most understanding spouse.

What I've learned is that amplification and loudspeakers cannot each be considered in isolation - it's as if they are a single component.
If you're not wedded to very deep bass (the aspect of reproduction I'd personally compromise on in your stated price range), loudspeakers in the range of -3dB at 50Hz, augmented by proper in-room placement, will give you a very satisfying low end leaving out very little musical content for most genres. Also, there are a number of nice integrated tube amp choices for $500-$1000 used, such as the Consonance Ella (I've owned one). If you've no experience with tube amps, know that bisaing is really easy for most and that their "extra maintenance" versus solid state is, IMHO, generally overstated.

Just a bit more grist for the mill, FWIW...

Good luck,

jb