Piano recording is my speciality - this is what I do..........
If it's a grand you really need omnis - and that's real pressure microphone omnis, not an omni made up from back-to-back cardioids as used in a switchable mic.
The distance and position will vary from piano to piano, room to room and music to music, so don't get tied down to a specific set-up.
I tend to prefer 20cm spaced omnis at around shoulder height at a distance from the piano. The distance will depend on the acoustics, the piano and the music.
Get the pianist to play and listen with your ears until you find the place where it sounds best to you - then stick the mics where your ears were - 9 times out of 10 this will be the best position.
My preferred mics are the Sennheiser MKH 20s, though my current project is being recorded with Neumann KM-D omnis (I have both 183 and 131 heads) and my new project in the spring will be with the new MKH 8020.
The picture shows the first recording session with both the MKH 20s and the KM 183-Ds - the CD will be with the KM 183-D. The KM-D are vertical because the 183 is a diffuse field mic. and the recording is in the nearfield - vertical means they have a flat response at 90°.
I hope this helps.