I love my Byerdynamic DT 880s which I bought quite a few years ago. However, I prefer listening to speakers then having headphones on my head. The only problem with your suggestion is that when I use the headphones, it's usually because people are around me who do not want to hear the music as well ;-)

I am still tinkering with transducers on my piano soundboard so that the piano itself is the speaker. It's been a project...

Also have 560s and 598's

I prefer the 560s for general music listening. They are excellent with Pianoteq, but the 598's are slightly better. Then again have had the 598's for 10 years+ so maybe I am just used to the sound.

Back to the original question: Good headphones are important, make sure they are physically comfortable to wear as well, and I prefer open back to close backed headphones.

"Good" is a much banded term.  I find Stagg SHP 2300 are excellent especially at their silly price.  The SHP5000, more expensive, are not even half decent.  I'd previously bought several more expensive 'phones, and managed to sent them all back fortunately, but you get tired of doing this, simply because you can't demo them.
Stagg 2300, £12.50 on ebay.

I prefer the 560s for general music listening. They are excellent with Pianoteq, but the 598's are slightly better. Then again have had the 598's for 10 years+ so maybe I am just used to the sound.

Back to the original question: Good headphones are important, make sure they are physically comfortable to wear as well, and I prefer open back to close backed headphones.

I ended up trying out Sennheiser 650 and 560S.  The 650 was more expensive and I expected it to be better, but surprisingly I substantially preferred the sound from the 560S.  Actually, I was surprised that I could tell much of a difference at all, but the difference was substantial. So I got the 560S.

I have the 560S as well. For the money it’s insane. Mixed 2 albums with it.

What you need from headphones or speakers depends, of course, and 'nice headphones' need not mean 'nicest headphones.' If you really need new headphones, I suspect you can tell, but how much you might benefit (or not) from premium ones, I can't guess.

Nowadays, I really don't prefer to use my MPOWS very well when playing any digital piano-- none too expensive and probably not a 'neutral' tone.

I had a pair of closed-back headphones by AKG and they definitely worked. But then when I wanted more headphones, I got open-back Koss Sportapros, which left the AKG set with a sense of being not as good... though the AKGs still seem reasonable.

Incidentally, the AKG was more like $200 and the Sportapros like $40. Sportapros can come up excessively tight against you and that can be a problem sometimes.

I might get Senn 6XX or something eventually... I've no need to hurry on it.

1.  Sound sources in the lower frequency ranges, ie.: low notes on a piano are rather omnidirectional ... quite spatial

2.  Sound sources in the mid to upper frequency ranges, ie.: mid to upper range notes on a piano are quite identifiable as to their presence - location - our auto location tells us that.  This is analogous to optical parallax resulting from two eyes.

3.  Having a set of speakers with good quality low frequency capabilities played simultaneously with a good set of "open sided" headphones is a remarkable combination.

4.  My headphones of choice have always been the Beyerdynamic DT-880.  I bought mine from their service center in USA/Mass for $110.  New ones are in the $300 range.

Kindest Regards,

Lanny

If one wants to get the best sound out of Pianoteq when practicing live, how important are the headphones?  I listen on a pair of Sennheiser HD 202,bought them many years ago.

You're not really getting the value of having Pianoteq if you don't have decent headphones.

You can get former flagship headphones like the Sennheiser 650 (6xx) for $200 on drop.com.
https://drop.com/buy/massdrop-sennheiser-hd6xx

Even the 30 years old Sennheiser 580 (58x) is still excellent for $140.
https://drop.com/buy/massdrop-x-sennhei...headphones

Just be mindful that they are relatively "high impedence" headphones, ie they may need a higher voltage than older laptops used to provide through their headphone jacks. I've used both with an ipad and they're fine for normal listening. Current macbook laptops are advertised as being high impedence headphone friendly.
https://support.apple.com/en-au/HT21285...lts%20RMS.

If one wants to get the best sound out of Pianoteq when practicing live, how important are the headphones?  I listen on a pair of Sennheiser HD 202,bought them many years ago.

It's worth getting headphones that sound good enough, and most importantly are comfortable for long sessions.

Great sound is much more than a bonus but it's still secondary with headphones!

There are big differences in sound quality. Best to find some way to demo several pairs.

Look to higher impedance models, and a sound interface to drive them.

Sticking to Sennheiser have a listen to some 600 & 800 series. Also perhaps check out some planar designs. Circumaural designs. Make sure you find them comfortable on your head, that's the main thing.