Mellow speakers for a digital piano

Seriously, try out a reverb. Its highly likely that is part of the sound you are after.

This will teach you not to post questions regarding pro audio on a high end audio site :) :) I'm sure the resulting confusion was worse than before the question was asked :)

I was assuming this was for home use, and was going to suggest Wharfedale Diamond 8.1 or 8.2 which have no treble at all. Failing this the Q Audio lower range stuff has a dull sound...

Pro audio gear is typically not laid back sounding unless the tweeters are blown... EQ will change the sound. However if your keyboard is midi capable, you could use it with software that will let you choose the piano sound you like and apply processing to this sound, such as reverb, in the digital domain.

you can go to aliexpress then i think you get it https://thevideoder.com/

To paraphrase 

dont shoot me
i am just an audiophile
with a piano gig on the side

I use Genelec 8020 active monitors with my Nord Electro 5 and Korg Stage V1 tube keyboard. I also have a Traynor K4 keyboard amp with tubes.

http://traynoramps.com/keyboard/product/k4/

I’d say you need tubes if you want a sweeter sounding piano. That or a much better piano.

The above combo is ideal especially as the Korg has proper weighted piano keys and the Nord has organ style keys - I can midi out from the Korg to the Nord keyboard as well as split the keyboards to have two different sounds simultaneously.