Also, on the HDD issue... as long as it's in a separate cradle, who cares about the weight? If you're carrying it in your pocket, don't take the cradle. If you're on a road-trip or dj-ing, then who cares about a couple of lbs of weight?? ...and if you really do care, then don't use it! Even a 2.5" HDD isn't enough to hold all the tunes in my stash or those of most of my friends.
If you don't care about the weight, why mess with a dedicated audio player at all? Bring a laptop computer, maybe one with dual hard disks, or an N2, or get one of those 3.5" media player HD enclosures and control it with a PDA. You can even put a 750 GB SATA drive in some of those, I think.