The Z1000 brick by itself can be used with the TIU variable channel, but you will get the same results as with the PH-180. If you use the Z1000 brick with it's Z-Controller then that should not be run through the TIU. It should be connected to the track separately.
I think I would also disconnect the TIU outputs to the track while using the Z1000 with it's Z-Controller. Not certain about this one, but if it was my setup I would do it just to be safe and protect the TIU.
I haven't tried doing anything like this before, no personal experience. My layout is all command control all the time, I don't have any conventional only items to even try it with. That's my main reason for trying to be careful with the TIU here and I wouldn't want you damaging yours either.