Does this look like what you have?
This helps to "extend" the zigbee, but it should be closer to the processor, rather than at the other end of the house.... think of it as a relay race..or a hand off of such. Try bringing the zigbee extender, if that's what you have, closer towards the processor. Within 40-50 feet would be optimal. but Ive seen them work further without obstructions. The zigbee will have to readjust after this,. This may solve your issues, and may not.
If you take the remote in the closest room to the equipment, closer to the processor does it find the network..?
I still run an HC800 for my entire house, but I also have 40+ dimmers and switches and thermostats so my mesh it very solid.. I wouldn't give up on the 800 yet.
You do have a very sparse setup (zigbee wise), and the recommendations for Z2IO and other dimmer/switch additions are great suggestions. Especially since the Z2IO are on the hardwired network and would act as repeaters for your processor which equals better coverage away from the equipment.
** You still need to find the version of the OS on the processor ie.. 2.53, 2.6, 2.9, 2.10 etc...
I would like to see you have a better experience with Control4 than what you have gone through recently, so id be more than happy to look at your system remotely. If you want you can PM me and I can explain how we can do this.