Hi Mikhail,
On my knowledge of recording methods, I have to credit "marik", one of the other members here (and an incredible pianist) with giving me a crash course when I was evaluating digital recorders. He happened to listen to a couple of my past recordings and noticed immediately that I had been using a close-in method. That, in turn, led me to do a lot of reading on the subject on my own.
I hear you on the Yamaha C3 mechanical sounds when recording. One thing I like about Yamaha, having tried the C5 a few times, is the extraordinary evenness of its action. I also like the feel of the key tops--they more approximate the feel of ivory than the other plastic keys you encounter today. But yes, those pianos seem to start off bright when brand new, so only get brighter over time. I think your solution, through experimentation on mic placement, will definitely be to move your mics farther away in front of the piano to leave the percussion zone. (Do your measurements from the front leg of the piano, not the curve.) As I say, in my living room it took a distance of 8 feet to get blended music without percussive effects. Start at 5.5. feet moving outward, do short test recordings of the same piece of music for best comparison, and you'll surely find what distance will best work for you.
Very often mics are sold with interchangeable capsules. So if you now have Samson CO2 cardioid capsules, and if you go back to the source where you bought them, I would bet you can likewise get a pair of omni-directional capsules sold separately from the mics themselves. All you need is those capsules. In fact, you could even take a quick look on Ebay to see if any are for sale there at a bargain. Once again, when you start moving the mics away from the piano, it'll reach a point where the cardioids can't work effectively--just too far away from the sound source. They're only good for close-in due to their inherent design.
Glad you enjoyed the Prelude No. 7. But don't forget to listen to No. 8 here on Page 1. That's the more important recording, because the set-up was done properly, whereas No. 7 was done close-in, which was the improper choice.