I have the 606 S2 AE and I find them a tremendous speaker. I’ll briefly outline my journey with them and then add the caveats.
Firstly, I’ve paired them with all different kinds of amplifier. I’ve used them with Arcam, which tame the highs you dislike, but the overall sound was a bit, well, boring.
I’ve used them with Rega amps - 2017 Brio and Elex-R - with great success. They’re rhythmic, musical, and highly enjoyable, but if you’re finding them fatiguing, Rega won’t cure them.
As a curveball, I tried them with a vintage Musical Fidelity A1, first 7W in Class A. This is a very luxurious and musical combination which takes away the fatigue, but it’s not the last word in definition.
I contacted B & W who now recommend the Marantz 6xxx series or 8xxx amplification (obviously, as they are now stable mates), but initial demos were done with ROTEL amps, namely the A14.
I still have them. They’re now on the end of a World Audio Design KEL 84 valve amp, and it’s glorious.
They’re now on are talented speakers and, if you’re finding them get it right, will reward like no other at the price point.
However……..
This is in my room, with my music and my ears.
If you have decided these speakers aren’t doing it for you, all the box-swapping in the world isn’t going to change the essence of these speakers.
I persevered and made it work. Only you can decide your path.
Speakers, and the way they interact with your room and your ears, is the most important link in the hifi chain.
Trust your ears. Nobody else’s. And remember, you’ll know when you’ve got it right because you’ll smile, cry, tap your feet, sing along and always find time for one more album.
Good luck.