What's the maximum size for songs/ambiance?

I tried to put Bruford - Forever Until Sunday in my level (after converting it to .ogg and adding the appropriate music credits) as Song2 but KS+ just played the default Song2. Is there any upper limit to how large a song can be in filesize? Or anything else that might restrict it from playing?

As far as I know, there's no hardcoded size/length limit for music tracks in KS. Is your Windows system configured to hide file extensions for known file types? If that's the case, maybe your file has a redundant hidden extension (e.g. something like "Song2.ogg.ogg", but the file manager shows it as "Song2.ogg") that causes KS to not find the file even though it can be opened and played with other programs without issues.

Did you experience this problem only with the mentioned track, or does this happen with any song you try to encode into Ogg? If it's the latter, maybe the tool you're using for this task has a default bitrate/quality setting that makes the output file incompatible with KS somehow. Try fiddling around with the codec options (if available) and see if this makes a difference, or just try a different program. Audacity's built-in Ogg Vorbis export function works fine for me.

Audacity's export function seems to have done the trick. Thank you!