One thing that really annoyed me on my previous two-zone preamp was the inability to adjust Zone 2's volume and then immediately adjust Zone 1's volume. It would stay in "Zone 2" mode for about five seconds before reverting back to "normal" mode. Yes, for five seconds, it would adjust the Zone 2 volume even if I used the Zone 1 volume buttons. It's a very minor detail, but very annoying to both me and my wife. It'd be hard to know that without testing for it specifically, but it's something that drove me to buy a new preamp (well, one of a handful of things).
Another thing that I've not come across that would be nice is the ability to use a digital input for Zone 2. I only have direct access with three preamps (Outlaw 990, Maestro M2, Cary Cinema 11) and none of them will convert a digital signal for output on Zone 2; you must use an analog input. Normally, I wouldn't run analog L/R from my DVD player, PC, etc., but I do now because none of the Zone 2s that I've used have DACs on Zone 2. Unfortunately, I doubt you'll be able to find one that can get around this...
FWIW, I'm also using a two-zone preamp in a three-zone application (main, family room and patio). The patio is connected to the family room, and their volumes scale together. I have a volume knob on the patio that controls the levels out there. When no one's out there, we just turn it all the way down. Of course, if you want music on the patio, you're also going to get it in the family room, but they are adjacent, so there's no disparity in the program material. Now, if you want one to be loud and one to be quiet, you'd have a problem. But the way it is set up now works very well for us.
Good luck.