Sansa c250 only does mono with plugins.

[Rydian]

I can't find the FAQ for this player model, and since this seems to affect plugins only, I'm posting here.  I searched, found nothing for anything like "sansa stereo c200" or "sansa mono c250" or any combo of those.

I rockboxed this a while ago, and have upgraded at various times.
When I noticed the issue, I upgraded (to a pre-3 version, the latest at that time, by manually unzipping into the directory on the player) and it fixed nothing.  When 3.1 came out, I upgraded to it (with the official utility you all provide), but then decided to uninstall rockbox (but not the bootloader) with the itility (assuming it'd remove all setting files and such) and then immediately reinstall with the utility.
So right now I've got version 3.1.

I first noticed the issue (before 3.1) when playing some NFS files.  Some main instruments seemed to be missing.  I assumed it was the artist sacrificing it to fit the format, but I played a few more, and noticed that really important things (like the main melody!) were missing on some.  I played these files on my computer and get left and right channel fine...  Also, videos only play the left sound channel, despite being in stereo.

When playing MP3 files I get stereo fine.

It only seems to be plugins.  I tried changing the audio settings around, like stereo width and setting the audio to mono and such, none of it seems to work.

How would I fully erase the settings on rockbox to start over, if that's a possible cause?

[Chronon]

There are instructions in the manual on how to reset your settings.  Have a look here: http://download.rockbox.org/manual/rockbox-sansac200/rockbox-buildch12.html#x15-28300012.3.3

[Rydian]

Thanks for the link.  That fixed the stereo issues when playing MPG files, but I'm still getting missing instruments in NSF files.

Example.

What sounds like strings coming in at 0:07 sounds fine on winamp on my PC, but they're nowhere to be heard in rockbox.

[Chronon]

It's possible that there's a bug in the NSF codec.  Someone reported a similar problem with SPC files a while back: See FS#9577.  You could file a bug report and make the problem file available for a developer to check.