What is the best way to tame a slightly bright speaker?

Think about room treatments also.Reflections on hard surfaces and glass will emphasize high frequencies.You can make your own very inexpensively.Experimenting with chair and sofa cushions at first reflection points costs $0.I agree that subwoofers can help take some of the workload off your speakers and smooth things out.

Thanks jtcf,  Yeah my room definitely needs some work.

Need to know which cables, power conditioner do you use one, power cables stock or aftermarket, high end rack or not, room setup, and of course what is your source.

What setup which works for one set of speakers may not work for another, so this might mean a retuning of the system.

Please feel free to contact us, we are really good at system matching and tuning. 

Dave and Troy
Audio Doctor NJ

Room treatment for reflections is high up the list.

Electronically, it would be to increase the resistor value in the tweeter’s high-pass filter on the crossover (e.g. go from a 2ohm resistor to 2.7ohm resistor). This would reduce the level of the tweeter by a db or so and leave everything else the same. But you’d need to be OK removing the drivers, crossover, and soldering. Tweeter crossover capacitors could also be swapped out for more boutique brands with a warmer sound signature. A couple of resistors would just be a few bucks. Boutique caps could get much more expensive depending on brand and values needed.

Otherwise, cable switching (or biwiring) could give you the normal audiophile "solution" to tone controls!

One might also consider a dsp solution for room eq.

A sub does not "solve" bright treble; it would rather change presentation if low end is lacking. Not the same thing.

TBH, everything except room treatment and the resistor change would be of dubious value for money in my eyes.