it is badly that I cannot make this topic in global field( I would like readers of CP4 also to come here

A) The main feature for me is a quality of piano sounds.

The S90 XS is a Stage Synthesizer - designed to be a 'quick access' instrument for those requiring a synthesizer. By 'quick access' you are able to create layers and splits on-the-fly when necessary. It features the Motif (sample-based) Voice Library, and 192MB of File storage which can be used to stream MIDI or audio files. While not as editable as the Motif-series from its own front panel, it is fully editable via the free downloadable "S90 XS/S70 XS EDITOR".

The CP4 Stage is a Stage Piano - the difference should should be clear - designed to be a 'quick access' instrument concentrating on Acoustic Piano and Vintage Electric Piano sounds (Rhodes, Wurlitzer, CP80, etc.); based on SCM and AWM technologies (SCM = Spectral Component Modeling and Yamaha's AWM Advanced Wave Memory sample playback engine). The pianos and e.pianos are made from some new advanced technology not found in the S-series or Motif-series. In addition to this concentration on acoustic and electric pianos, there are some 400 AWM sample-based sounds taken from the Motif-series.

If the main feature for you is quality of piano sounds... CP4 Stage. It features the Yamaha CFX acoustic piano (in addition to the CFIIIS and S6). In fact the CP4 Stage is the first time this Yamaha piano is available in a portable unit. The CP4 Stage is just 38 pounds, by the way.

B) Next is the comfort of play and touch experience. There are no such instruments in shops nearby - I have to order it only and I cannot try before the buy.

This is unfortunate, because "comfort of play" and the "touch experience" vary from player to player... Like trying on shoes, no one can tell you if it is a good fit, BUT YOU.

C) I have read that CP4 has wooden keys. Is it made for beauty or it improves the play experience in some way like soft tiking sounds of keys hitting the bottom or some weight advances easier or harder to push? does it mean that S90 XS which does not have wooden keys has worse experience?

I have to smile at this one... While beauty is always part of the design concept, the white keys being made out of wood has nothing to do with its looks. It is 100% about the feel. You have to press a key and hold it down then look closely to see the wood... I'll bet many people play the CP4 Stage never knowing the keys are wooden, they just notice they really like the feel (weighting and response). "Touch" is at the core of the CP4 Stage's design... It has NW GH3 action. Natural Wood, Graded Hammer Triple Sensor action. This gives it a more realistic acoustic piano feel. The 3 sensors mean that much like on an acoustic grand, the key does not have to return completely for you to retrigger it. Most electronic pianos have an action similar to an upright piano, this triple sensor function makes it more like a concert grand. "Touch, Tone, Technology"

The S90 XS has Yamaha's "Balanced Hammer" action... All keys have the same resistance across the entire range. Being a synthesizer this works well for non-acoustic piano sounds... It also features AfterTouch, again because it is a synthesizer!

D) technical features - If not to think about synthesizer feature is there else something better than in CP4?
E) Which of them could better support additional pedals like on old wooden pianos?

Being principally a piano the CP4 comes with a Sustain Pedal, the S90 XS does not. Both can handle the Yamaha FC3 Sustain function which instead of being simply ON or OFF sends continuous vales from 0 through 127 allowing very pianistic response to pedaling. Both have an assignable foot switch jack that can accommodate a second pedal for Sustenuto.

F) Why S90 XS is more expansive then CP4 is it marketing or it is really better? I understand that they are different in the field of their use in musical world, but does CP4 include everything that is in CP4? Can I say that it has same features and even more?

I'm sure this contains a typo... Asking why one is more "expansive" or "expensive" is like asking why an Apple is more than an Orange... I can't give you a better answer than they are different fruit. These are different keyboards, with different target customers.

Wish you could get to a dealer and try them - it is really all about your experience with them. I hope some of the answers above help. Asking someone which *you* should buy is just a poll of other people. Only YOU can know what you need.

One is a piano with a selection of complimentary synth sounds, the other is a synth with quality piano sounds.

The CP4 Stage is a Contemporary Piano built for the professional stage musician. The CP4 Stage is easily the best stage piano Yamaha has ever made!
The S90 XS is a Stage Synthesizer - a Motif without the Integrated Sampling Sequencer. The S90 XS is a Motif (known world wide) without the built-in sampler and without the built-in recording sequencer... There is no apology about the sound here, thousands and thousands of musicians prove that every day

If piano is your main thing... Then it's easy... The CP4 Stage.

Thanks a lot Bad Mister!

Forgive me for my typos.

Yes I would like a fine quality piano sounds, but ... 😀
I know it sound mad: I am afraid that I will become bored with only piano one day 🙂
But I so like the relaxing feel of good piano...
And badly, I can't get them both
Sorry

P.s. and in point "F" there also should be written: but does S90 XS include everything that is in CP4?

By the way
1) can I use both with a computer? or only S90 XS?
2) is it compatible with new Windows 8.1 and near future Windows 10

1) can I use both with a computer? or only S90 XS?

Yes, of course. The S90 XS is 16 PART multi-timbral via MIDI... the CP4 Stage is 3 PART multi-timbral via MIDI. You don't say what you want to do with a computer, but both connect via USB to a computer. You can download and read through the manuals (Yamaha makes all the Owner's Manuals and Reference Manuals available) for free download:
http://download.yamaha.com

Both can record and playback stereo audio files to/from an attached USB drive, no computer necessary.

2) is it compatible with new Windows 8.1 and near future Windows 10

Nothing is compatible with the "near future" yet... but unless Microsoft completely disregards musicians and music making, you can fully anticipate that, yes, even "future" Window 10 will be able to do MIDI and audio, and if that is the case - you will be able to connect your Yamaha keyboard to your computer.

....but does S90 XS include everything that is in CP4?

No. It does not. they are two completely different instruments. I think I explained the different technologies involved. The CP4 Stage has new tech, not found in the S-series or the Motif-series. This technology was developed specifically to model acoustic and vintage electric pianos!!!

Thank you Bad Mister, Your words will help me when I will make a final decision