Mellow speakers for a digital piano

It doesn't get much "sharper" (and fatiguing) than Focal monitors IMO. Get yourself a decent class A or AB amp and some Wharfedale Dentons.

Yes, they will be much more mellow than the Focals, but not veiled. Give em a go. MD gives you 60 days to test them out.

If you want to stay with active speakers and depending on your budget, you could also consider the KEF LS50 powered version. You will probably end up spending about the same amount by the time you add the cost for a preamp/amp combination to go with the Denton or any other passives.

Really? It takes $1800 worth of amplification to power some passive Dentons? I think not.

I'd go with this:
https://www.amazon.com/Yamaha-S801SL-Natural-Integrated-Amplifier/dp/B00N30M2DW

I have yet to encounter another brand that produces as realistic piano tones.

That's where these amps excel. 

I was just going to respond about the various options now beginning to sound like there is no reliable option ... only what various users have experienced and were happy with.

This is just the issue. The gear I recommended is solely based on what I've heard and what I believe might meet your needs in terms of tone. However, the MD rep made a valid point. Some home audio gear doesn't play well with instruments. Your best bet might be to take your speakers down to a Guitar Center or some other pro audio shop and see of they'll facilitate some comparisons with their monitors. I have yet to encounter a powered studio monitor that doesn't have an irritating top end, but they could exist somewhere.

In the meantime, you might try placing a piece of tissue paper in front of the tweeters of your current monitors. Not on the tweeter, but stretched across the opening in the baffle. You might be surprised by the results.

Good luck.

No, he needs to throw a lot of money at a hi-fi solution, tube amps and such. Definitely needs some shiny new gear from one of the resident dealers. There’s no way any pro audio gear will solve the problem.