Due to a problem with the template-haskell package and Cabal, you cannot cabal-install the emgm package with GHC 6.8. However, take heart! EMGM works very well with GHC 6.8. You merely have to download the tar.gz package from Hackage yourself, build it, and install it.
I thought I had seen you mention a workaround for that issue, but if not, perhaps you might want to add your experience to http://hackage.haskell.org/trac/hackage/ticket/326 Cabal should support Cabal-version-dependent Setup.hs There's a sketched hack-around at the end, using Setup.hs only to call to separate Setup-version.hs files, to circumvent Cabal API instabilities. Not nice, but perhaps better than to bypass Cabal alltogether? One would also have to pass parameters, and the Process API has changed in the meantime.., which I why I still think Cabal itself should simply be able to pick cabal-versioned configuration and setup files, if they exist. Claus