Multi-room capability isn't new. I have an Onkyo HDMI receiver from 2007 working quite well with dual zones, and the volume control for the second zone is on the front panel. These can be found fairly cheaply these days since they're not 4K. Other brands offer similar capabilities.
If it's not correct, you should be able to find one fairly cheaply on ebay. You can extend the sensor wires as well by making or buying an extension cable with the correct plug and jack, although I don't know if you can use more than one sensor at a time (e.g. to be able to control the system from either one of your remote rooms).
I have an extender that works really well with remote zones. It's a battery in a sleeve that goes in the remote. The sleeve is a transmitter that counts current draw pulses. It transmits these pulses to a small base unit that receives these pulses and converts them back into IR. It sounds weird, but it worked with every device I tried to control. This takes the place of the 'optional IR sensor' and requires nothing to be hardwired. Another nice thing is that it eliminates the need to be near a remote IR sensor. I used mine in a universal remote so that I'd be able to control the receiver as well as components.
I had one of those as well, used to be marketed under the name of Leapfrog. I agree, it works well.
That looks good. It'll give you the stuff you need without the surround part of an AVR. I'd forgotten that most of the big manufacturers still have a decent 2-channel unit. I'm sure it'll sound fine for your setup. Assuming the quality is also good, I'd def consider it. Add the battery extender thing I posted above and you'll have a nice multi-zone setup!
