0. raised volume to +2dB
1. switched to binaural mode
2. switched off all effects
3. set hammer noise, spectrum profile, impedance and damper position to the values Don suggested, and tweaked them a bit
4. switched back to mic mode
5. put mic 1 and 2 more distant from the board
6. switched on Reverb, added a bit more wet and lowered tone parameter
7. added some compression (standard Ableton Live compressor)

Now I finally realize how much Pianoteq timbre is richer and more alive than Galaxy D!

(perhaps It's worth mentioning that I actually have a ear problem (bilateral otosclerosis) that limits my frequency response (-40dB peak at around 800Hz). I completely forgot about that problem before, and that's probably the reason why I am over-sensible on the contralto frequency range: doctors explained that some kind of over-compensation often takes place in such cases)

Thank you very much for your precious help, and happy 2018!
Fabio

I also see much potential with binaural, but it always sounds a bit 'closed' to me.  I wish that the 'microphones' in the binaural head could be tweaked to make them more live, more airy, or similar.

I agree,
I prefer a Player perspective of the microphones that gives à fuller and more open sound.

Any advice on how to tweak Pianoteq parameters to obtain a sound that is similar to the first fragment would be very appreciated.

Many thanks again for your time,
Fabio

I don't hear a nasal sound. Galaxy has a deeper sound and is flatter. Pianoteq sounds more lighter and more detailed.

If you're using the Pro version I'd edit:

VOICING:
Hammer Noise: 1.40
Spectrum profile: sliders  [3] -1.00, [7] +0.50. Note edit is more complex but worth a look.

DESIGN:
Impedance: Between 0.90 and 0.95

OUTPUT:
Action: Damper position: 1/7.0 or 1/8.0

These will flatten out the sound, then you could tweak details back in using other enhancers. Like Piano, Mezzo and Forte.

Not exactly on topic, but up to it to some degree: https://youtu.be/MTQ3j70P9es

(and, curiously, the Pianoteq with these changes sounded more 'present', whereas the Galaxy sounded a bit more shrouded, as if it was playing through a curtain)

Like I said, if I test 100 models, I bet I will like no one, just like when I went to TV store and find all LED TV (LED backilight) as crap.

I could tested more 5 headphone models, but would not buy anyone, and the seller would get pissed off imaging I was making hin of fool.
I still can't explaing in words why the phones are not so bad to listen music, but are horrible to use to play digital pianos.

Pianoteq will always be "artificial", it's been like that for the past 10 years, not sure why anyone things it will ever stop being "artificial". It's code, not an actual real piano (but it still sounds like a really good piano)! Just like sample libraries will always be static snapshots of a sound played at one point in time. Both have pros and cons, and both will continue to have pros and cons. But, Pianoteq's pros heavily outweigh whatever pros sample libraries might have, first and foremost, I cannot find myself inspired with piano sample libraries, at all... With Pianoteq, I can play endlessly, like on a real piano. THIS is where it's at.

So it may be true that those dissatisfied with the Pianoteq sound either have golden ears or exceptionally good equipment, or both. After over half a century of playing acoustics, I get a great deal of satisfaction from PT6 - mainly the Grotrian for Romantic music and the SteinwayD for Haydn, Mozart, Beethoven.

I am not qualified to give advice on sound, except the simple process of using one's ears and patience. Oh, and has been said, add a more distant mic. Pianoteq has so many means of adjustment, settings can be found for all acoustic situations/equipment. It's a long learning curve but worth it IMHO. Plus, leave a reasonably good setting for a day or few. Our ears are not instruments that work consistently in all conditions.

a) Most important. Don't use high quality speakers/headphones, better use somewhat cheap semi-full range computer speakers. The better monitoring system you have - the more clearly you'll hear the artificial nature of the Pianoteq in its current state. Cheaper speakers help masking it. As an alternative solution I could recommend using some tape-vinyl emulation plugins, but I'm not a big fan of it.

d) Don't underestimate the overall volume settings.
e) Dial the dynamics.

f) I would definitely recommend some decent audio interface like something like RME for it's superior drivers stability at low buffer sizes, but still stick to point a) for the playing experience.

...or, actually, to be fair, I would not bother really.

+1 on AKG K702 headphones.

Thank you very much Joe (and others) for the recommendation (AKG K702) and the comments about a separate headphone amplifier (which I happen to already have do not use). I’m not very happy with my current headphones (Sennheiser HD600) which has some annoyingly exaggerated volume and resonances for some notes and small ranges in the mid to upper treble. Anyone compared the AKG K702 to the AKG K712 headphones?

And an aside: your version of Bach’s Brandenburg concerto using Organteq is magnificent!

Of course, important thing to note is that with headphones, Pianoteq's output section should be set to Binaural...

This is a very important tip. Thank you, EvilDragon.