The second one about an underrun detection is a bug/fixme in wine code, since I get those constantly. I think all it does is result in some choppy sound; there's nothing to do but wait until they fix it, or fix it for them if you know how
The one about MCI... Check your wine config file (should be in ~/.wine/config), and look for a couple lines under "DllOverrides" that say:
"mciavi.drv" = "native, builtin"
"mcianim.drv" = "native, builtin"
If they're not there, add them under "DllOverrides". If they are, then I do not know what to tell ya. It could be another bug within wine; usually the errors that say "fixme" are intended for the developers of wine, so if it's not causing any problems in apps you're running with wine, I wouldn't worry about it much.