I'm with Angelina on this one; if one really knows what they are doing, it is possible to get a beautiful sound on any piano (unless it is JUST GOD AWFUL..like the worse .00001% of pianos on the planet). Besides, you can control dynamics on any piano, and since sound quality is basically a heightened manipulation of dynamics, timing, and pedaling, it should be possible. Of course it will not be AS GOOD as the sound of a Steinway grand, but you should still be able to achieve your sound ideal.

I think the answer to the original question is that different sound qualities on the piano are the result of different amounts of pressure being applied to the key by the arm. Before you strike a key with your finger, you should be able to already know by the feeling in your arm and the amount of controlled tension how it will sound. Try to experiment with different types of attacks and arm pressures until you hit the jackpot. The key to all of this is having a free arm but firm fingers, and, most importantly, a discerning ear.

Another thing I would recommend (I know a lot of people are against this), is to listen to a lot of recordings of pianists who have a warm tone. Gilels, Cherkassky, Horowitz, Nyierhyazi, etc. Don't try to imitate them, rather just listen and listen.
I remember watching the way Gilels played a single note in the video of appasionata that changed my playing forever..
Since 90% of piano playing is in the ear and mind, the clearer our mental image of what we want our sound to be is, the greater our body will find it's most natural way to express the sound you want.

Good <> amazing/great.

You can get a good sound from almost any piano. But good is always in conjuction with the piano you're using.

I mean, if this general comment was true 100% then we should also be able to get a great sound from digital pianos as well! LOL!

I have heard many excellent pianists complain about pianos that are far better than anything most of you would ever play.

May be that's because they're just missing their old college practice room pianos?

To the original question ... no one has mention this one yet:

Try using the una corda pedal. Don't step it all the way down; just step it down a little bit, just enough to shift the hammer grooves off the strings by a little, but still hitting all strings.

It's just one more thing you can combine with all the other things that have been suggested. Good luck exploring.

"Warm" has been used to describe many things, but I see it refer to one thing the most: loud fundamentals relative to overtones. For a pianist, that means slower strike velocities (i.e. softer playing) and using the una corda pedal so that softer felt strikes the strings. For technicians, it means softening the hammers.

I'm talking ONLY about sound and its quality. If you are capable of playing a nice, round loud sound on one piano, you should be able to produce the same type of non-ugly, non-harsh sound on another piano. Doesn't mean it'll be easier to play or that you'll sound the same on a crappy piano.

I know perfectly well that some pianos should simply be lit on fire =) It would be better for all of us......... Especially steinways with no upper register

I play on such pieces of work every day

In fact last year I heard a young, very very talented pianist give an entire recital on a crappy little upright in a church, and he sounded like a god. With stuff like Appassionata, Ravel Miroirs and some Rach.

Also isn't it funny how Richter didn't care what he played on? And he always sounded amazng =)

Is someone able to upload two recordings (or videos) of the same piece on the same piano, one played with a "warm" tone, one without, to demonstrate ways of achieving this?

Like recording is soo accurate.