My results have also been more mixed than i originally thought. Smashing Pumpkins - Mellon Collie (24 96) worked fine once i changed the file extension from aif to aiff. However, for the life of me I can't get other albums to show in the Pono Player library after they sync onto the device. This is whether they are "aif" or changed to "aiff" - these include Wilco - Being There (aiff, 24 88.2), Santana - Abraxas (aiff, 24 88.2), Bob Marley - Legend (aiff, 24 96) or David Chesky - Jazz in New Harmonic (aiff, 24 96) to work - whether they are "air" or "aiff".
Other "aif" and "aiff" albums work fine - both low and hi res - such as Beck - Sea Change (aif, 24 88.2) and Beatles - Abbey Road (aif, 16 44.1). i don't see a pattern.