Is Shure SRH-440a great headphone for digital piano sound???

I don’t think you will have distorsion issues  with these headphones . The critical point is whether you are going to like ´the colour’ of the Shure . In fact there is no colour , so you lay feel the sound lacks character specially in the upper register . It really depends upon your personal liking and only you can tell if you like the sound or not no matter what other reviews or users tell you .
As you mention , make sure the headphones are not fake , as there a lot of fake Shure in the market and they look incredibly authentic.

Not directly an answer to your question, but I'm very happy with my Hifiman Sundara - decent bass extension, undemanding on the audio output, and distortion-free. I picked it for the clear midrange and treble which is useful for the piano. It's good value for money.

In general, I agree with the others that personal preference is more important than technical performance in headphones - whether you like the sound signature or not is something you can only decide for yourself. But having said that, my experience has been that you can get close to any sound experience you might have in mind with a digital EQ: you don't need to pay extra for headphones just so that they meet your preferences out of the box.

what I meant is that it was made for studio  monitoring and therefore is very neutral . Some people prefer headphones with more sound colour for piano . It is not related to the price , you will find expensive neutral headphones and expensive ones full of character . It is all about the use case and your personal taste .

I have found I much prefer open-back headphones for piano practice. The grado models are great for this (those are what I use). The Shure SRH-440 headphone is closed-back. I definitely recommend trying an open-back for comparison.

Regardless of which brand of headphones you buy…

I just want to say why I like open-back headphones, what they are good for. Maybe it will bring up things someone hasn't thought of.

Good for critical listening, enjoying high-quality content, mixing content.

What they are not as good for (but these things don't bother me because they don't affect me when I'm sitting in my little room alone)   
Blocking outside noise (I don’t need that option), listening while traveling (don’t do it) using as monitors when recording with microphones (don’t do it) they leak sound out (I’m alone when recording)

Many expensive high-end headphones have open-backs because they sound more natural and clear (when there is no ambient noise), Because I don’t need to isolate myself from noise I’m using open-back headphones.
Ever since I started listening to music and trying out headphones at the age of 12, open-back has gradually become the winner because today I’m always alone in my ”studio” and don’t bother anyone.
This is what I have experienced and learned.

Best wishes,

Stig

I second that, open-back headphones have been a revelation to me in terms of soundstaging and clarity. I also find them much more comfortable to wear for a long period of time.

For pianoteq purposes I actually think it's an advantage that they don't block out sounds from your environment: makes it all sound a bit more integrated.

Ah sorry to hear that.

During my research, I found the Rtings comparison table to be useful - it helped me find an accurate, low-distortion, low-colouring pair of headphones in a good price range.

https://www.rtings.com/headphones/tools/table/175685

Incidentally, the Shures aren't doing particularly great in that review set - so you may actually come out of this with a pick you'll like more

I looked at the list and searched for Grado (225) and here is their opinion (but we all hear different so it is best to test it yourself first if possible)
I had a longer explanation about how we hear and why we hear differently as we hear, in another post. Why someone like a headphone and another not.

”The Grado 225e are good for neutral listening. They have a spacious soundstage and a good reproduction of instruments and vocals. They lack a little bass and may be slightly sharp at times, but they reproduce the detail in high-res audio with above-average accuracy”. Whatever I buy I try to test it first if possible.

Best wishes,

stig