Well, I can't really see the point in not switching the formats, if it's clear that one format (Ogg/mpc) beats another (mp3).
As I said, the (current) improvements are negligible and not worth due to compability issues (friends and other people not having OGG/MPC-capable players for instance -- yeah it's their fault but it becomes your problem).
There may not be point in changing all your music to the new format, but why not support it in future? I for one make sure that I'm ripping with the best quality-size -ratio (by the way, why are you using CBR and not VBR/ABR?).
Re-encoding a lossless format will NEVER happen for me.
I use CBR because it feels more reliable, I don't like the added uncertainty factor that VBR adds, and as I'm a quality freak, when I tested with VBR, most frame sizes stayed at the CBR level I'm using anyway. ABR is total crap and shouldn't be allowed to exist.
Hmm, I don't know if I see your point here.. Do you mean that they aren't popular or supported? For an individual using XMPlay with the plugin, it shouldn't be an issue.
I mean the improvements are more or less negligible (i.e. "the codecs aren't there yet --
in the future when everything's wonderful and perfect"). OGG isn't really that much smaller size-wise. At crappy, low bitrates yes. But I don't use those ear-killing bitrates. It has other merits though, like license-free and multichannel, but none of that is anything I care about -- yet.
It all boils down to wheter the improvements reach such a level that it's worth all the hassle. Simple.
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Oh, AFAIK, UMX is the original file, which can be XM, S3M, IT, FAR, MOD and some other, more obscure formats, inside an Unreal Package file.
However, it was impossible to have several mods inside that package, so it might've just been a custom header added to the original file, I never had to work much with the Package format myself (or it could've been a limitation in UnrealED/UCC, but that seems weird).