I have tested it against the Pioneer xdp-300r and the AK70MK2, the ZX300 wipes the floor with both of them, especially on the balanced output. To give you an idea, the balanced output is as good as the one on the WM1A (the WM1A has better SE though), keep in mind that the SE on the ZX300 is no slouch, the SE on the ZX2 is better than the one of the AK240, the AK70MK2 SE holds it ground compared to the ZX300's own SE (it's not inferior but sounds different, it's hard to describe without listening to both), the WM1A and ZX2 SE have a warmer signature compared to the ZX300's SE, if you value SE more the ZX100 has a similar (albeit slightly inferior) sound to the ZX2 at a fraction of the cost, and is slightly better than the SE you get on the ZX300 (although you won't have the high gain option that you do on the ZX300), the Pioneer xdp-300r SE is no match to the one of the ZX300.
Then again, using the balanced output, the ZX300 wipes the floor with everything I've tested so far except the WM1A and WM1Z, (the sound signature on the ZX300 is similar if not identical to the WM1A on the balanced output), the WM1Z signature is different, the WM1A is warmer but the WM1Z seems to be slightly more detailed, then again it's a matter of preference.
I also felt that the Kimber Kables lacked "power" somehow, so I settled for the cheaper Sony balanced cable instead.