The Marantz PMD661, although more expensive than a Zoom H4N, is a lot quieter in the input stages. If you already have an H4N however, a good external pre-amp like a Sound Devices unit should improve things dramatically. As for the Sony PCM-D50, you are correct that the 1/8" inputs are unbalanced. Its preamps are pretty good, but you still have to contend with small, fragile unbalanced mic cables and no phantom power. Unless you buy the external preamp accessory for it. I'm not trying to sell anybody anything, but this is one of the main reasons I ended up going with the PMD661.