Hi Leah. I just listened to the whole track and I thought it was outstanding. I do have several ideas for you to try. I've been a producer for a much longer time than I've been a composer, so my experience is much more oriented toward making things sound like the artist wanted them to sound. I thought the arrangement was really good, by the way, both piano and strings. The harshness in the Bösendorfer is exactly at 1kHz and 2kHz (I just checked it in a project), so if you put any eq on it, set the frequency to 1kHz (which is the same as 1000) and dip something narrow, like a Q of 4 or 5 (if you see Q on the eq controls, if not, don't worry) by 3dB, that will help. More importantly, I would stay away from all of the louder velocities in the strings and the piano. Use a lower velocity, and then mix the track louder (either with automation on the Logic Track, or with the expression, they're exactly the same audio result). The louder volume will still be perceived as intensity, but without some of the sample weirdness, which is just unavoidable, even in great collections like these. (By the way, excuse the long paragraph, I don't know how to format these yet.)
On the strings, I've been amazed at how much brightness I need to pull out of these strings. If you think about it, nobody ever hears strings like a microphone does, we hear them bouncing off of walls at a distance, and that removes a tremendous amount of the treble. I would use any EQ in Logic and take everything over 4K or 5K down a lot, maybe 3 or more dB. I've also been using the built-in filter in the Performance part of the VI interface, and at a setting of 90 or so (out of 100) it works pretty well, but the EQ is much easier.
Finally, beware of that ruthless meatcleaver, the Logic multiprocessor. It always sounds good as your tired ears finish the session, and only later can you hear the way it's massacring your hard work. Having said that, the track I listened to didn't sound that way at all, so you must have kept pretty good control over it. Great work -- good luck with it. Finally, I just reread the end of your post, the Bösendorfer on your track is not pingy except where you hit the louder velocities, I think it's a great sound for most of that track.
By the way, you can check out a much different vibe, but also Piano and Strings (VI strings, but before I had the Bösendorfer) at aotpr.com/ohana -- page way down to the track "Let It All Down". For VI solo viola and cello sounds, check out the track "Hidden".