you dont NEED any codec packs. win7 does it all, including most audio. you only need a mkv splitter if you have mkvs.
and there is no problem with installing divx, but only if you need it for extender use.
i avoid codec packs at all costs. becuase you never know what its is taking over. find out what you NEED and just install it.
unless you have a really good reason for switching codecs, like if something isnt working, dont change it, the PQ increase would be marginal, and could even be worse.
"If the world didn't suck, we'd all fly off."