I still haven't received my zx300, ordered on 26th of Dec from Sony, but I was in a similar position to you and wanting to evaluate this balanced headphone malarky.
There aren't a large number of 4.4mm headphones to choose from, I personally LOATH the Sennheiser sound signature... [rant]years ago I bought a pair of HD800 bcos they were all the rage and supposed to sound the best, with the best reviews, 5* all the way... well they sounded like murdering cats, only thing they consistently did was hurt my ears, make me hate music, and 100hr brake in BS didn't help!; so I when through great lengths to return that crap and I auditioned a whole bunch of Sennheisers, HD600 or 650, IE8, PCX... all sounded like terrible to me, then I found the Denon AH-D5000 and audio Bliss.[/rant]
So given that Sennheiser was out of contention, I was limited to Sony for native balanced solution; MDR-Z1R, MDR-1ABP and XBA-N3BP.
I got a good deal on the MDR-Z1R (A$1700/US$1330), so I'm waiting for those to be delivered. Historically never been a fan of Sony cans, I found them too balanced
, but they say the Z1R is pretty warm with some sparkle so I'm hoping they sound nothing like Sennheisers flat + screeching.
I'll update y'all once they've had +100hrs.