[Update: the book is Fool's Run by Patricia McKillip!]
Dear Internet, please help me find a poorly-remembered book!
It was scifi, likely published in the 80s but conceivably late 70s or early 90s. I do not remember much of the plot but I remember that there was a playing card motif and I think also a harlequin motif.
The most distinctive feature I can remember is that there was a virtuoso pianist who would occasionally go into a fugue state; I believe he was one of the main characters.
After ruminating on this further, I've added a few other qualifiers:
1. IIRC, the pianist is vaguely implied to be a reincarnation (either natural or technological) of Beethoven—or at the very least has a particular fascination with his works.
2. I think one of the characters is a red-haired woman? (I appreciate that this doesn't really do much to narrow things down when it comes to speculative fiction.)
3. It was very much a scifi book, not fantasy. Parts are set on a space station, I think.