The problem is, with a factory-build PC you get an OS with all the drivers for the included hardware, and sometimes (maybe nowadays it's easier) when you install a different OS on it you get problems finding drivers for hardware you don't know the name of etc.
Just a though

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I'd say go with Jello's offer, it sounds like a great machine (think about sound editing, that should run better on a high[er]-end machine too).