Hi Hye,
Thank you for your very kind comments on this sonata! I wish I could have played it better, especially where you listened three times! At the moment I'm trying to get a better performance of it, but today I failed in my quest, so feel a little down about that. Some of the textures are really dense, and it makes it really difficult. Maybe the next time I'll succeed.
There are a couple of factors that make me search for the repertoire I play. The first is that where I'm much older now, I feel no more obligation to be "a well-rounded pianist". I paid my dues doing that in my younger years. The literature of the piano is vast, and life is too short. So now, no more Baroque and Viennese Classical music for me, and very seldom will I play a Contemporary piece. I prefer instead to focus on the Late Romantic and Impressionistic periods mostly. The second factor in selecting repertoire for recording projects is this: I have no interest in presenting the 1,897,145th rendition of Chopin's Ballade No. 1 or other "conservatory anvil". What new insight could I possibly bring to such a piece? I love finding "new music" that is actually obscure or mostly forgotten works of great beauty written by worthy composers. That's what inspires me to my best efforts. And where so very few pianists play these pieces, I can contribute a little toward helping to establish the modern performance practices for such works. Playing many pieces of Bortkiewicz and Catoire was an honor for me, and both composers taught me much about playing the piano too!
Usually I become interested in a composer unknown to me by hearing a single work posted at a piano website like Piano Society. For example, Koji Attwood's live recording of Bortkiewicz's "Impromptu", Op. 24, No. 3 at another website inspired me to delve into this composer's music, and as I result I've posted recordings not only of the impromptu, but also of the preludes here. Similarly, I happened to hear Koji's performance of Catoire's "Etude-fantastique", and was immediately addicted to that composer's music. Yes, sometimes I'll find a recording. For example, Cyprien Katsaris did a Bortkiewicz CD, and Marc-Andre Hamelin played a Catoire CD. When a CD is available, I'll purchase it--and put it away for awhile.
I have found a lot of the scores at the IMSLP as well as at Pianophilia. There are also a couple of professional artists who have helped me out. In the case of this Medtner sonata, it so happened that I had the complete Medtner sonatas in my library (Dover Edition)... which had gathered dust. So I was searching through Volume I when I came across this Sonata-Elegia, Op. 11, No. 2, then looked into it. There is a lot of Medtner music that I dislike, so I am selective to ensure that I'll be motivated and enjoy studying and playing it.
I prefer to formulate my own interpretations, and allow just a bit of my own personality into it to put my own "stamp" on the performances so to speak. I prefer that the composer teach me the music rather than another pianist. As the last step, if I do have a CD (or can find a good performance on YouTube), I'll play it specifically to listen for any wrong notes, although sometimes I'm right and the recording artist is wrong (unless it's explained by playing from different editions).

But again, I would rather not be influenced by the artist's interpretation of the piece per se. So, for example, if you listen to my Catoire pieces and then listen to Hamelin, of course as a professional he is more virtuosic and polished in his playing by far. But more importantly, you'll find significant differences in interpretations. The same is true of Koji's Bortkiewicz "Impromptu" and mine, for example. They have marked dissimilarities which is a wonderful thing because it demonstrates the range of possibilities in interpreting music unheard for decades. Getting back to the Catoire pieces, one pianist told me that he was glad to have both my renditions and Hamelin's, as he thought that I brought out some of the features of the bass that could not be heard as clearly in Hamelin's playing. Another pianist upon hearing Catoire's "Etude-fantastique" asked me why I played it so differently than Hamelin, but added that he was glad that I had because I brought out more of the complexities making the piece richer in his opinion. So I'm always very happy to do my own thing, especially when the performance practices disappeared many decades ago, and need to be reinvented by the new champions of the composer(s). Many Late Romantic pieces need to be played from the inside out rather than from the outside in. And sometimes I find I have to discover the composer's visions and intents not in the musical notation, but between the lines of the music. Those are the kinds of pieces I love the most.
Well... I don't have a page turner here.

Our kids are all grown up and out on their own. My wife of 43 years dislikes piano, practicing, and classical music in general, so I practice only when she's away doing errands, and stop when she returns. So I couldn't possibly ask her to turn pages!
Thanks again, Hye, for listening to the Medtner and for taking an interest in my work methods.
David