For the AUR package, it hasn't been updated in awhile as it's maintained by a third-party user. You should flag the package on the AUR and inform the maintainer there's an update and post a link to the 32.0.58 thread. Otherwise you'll have to download and edit the PKGBUILD file yourself for the latest 32.0.58 build available (and you'd have to either calculate the SHA256 hash of the .deb file or edit it to SKIP).
IMO, I don't agree with the meta (or generic) jriver-media-center package being used on the AUR as it makes no sense, mainly because each major version of Media Center is its own standalone app with specific licensing. The meta package there is updated for every major version, which for example if a user is using only MC31 and didn't purchase an upgrade to MC32 it'll automatically update to MC32 which will cause users problems. It's fine if you always use the latest major Media Center version but an issue for those who skip versions. It should be jriver-media-center31, jriver-media-center32, etc. In my Arch Linux virtual machine, this is what I do locally and set pacman to ignore the jriver-media-center32 package that doesn't exist on the AUR and manually update it myself.
At least that's my two cents on the matter.
