I trust your 214 has the full ES and not the ES-T, right? With the ES, you don't have to go balanced, and there is no sonic improvement by doing so. You get a hotter output signal, better s/n ratio, and potential for longer-cable runs w/o signal degredation, or can go straight into the snake/console. All that said, unless the aforementioned helps your setup, going balanced doesn't really get you "more" than just using a good guitar cable into a proper DI.
I personally think the K4 is overpriced ...not a poor unit by any stretch, just overpriced, IMHO.
No experience with the Fishman but folks do like that unit.
you may also want to check out:
- Radial
- DTar
- Presonus (no preamp, just a 3-band para-EQ, but is dead-quiet and has balanced and unbalanced ins/outs)
- LR Baggs Venue
All these are strong units that are quiet, shape tone well, and enjoy good reputation for solid stage use. If you cant try them, try Sweetwater, MF, or the like who has a trial period. I'm guessing after you've picked the one that fits your liking/budget, any of the above will serve you perfectly well.
Edward