When you are in full penny pinching mode 😁 & sound quality is a priority, you could try the Schiit SYN full analog surround processor. (400 dollars)
It accepts analog outputs from any hifi DAC and is a full analog surround processor for music. You could also set something up based around a HTPC/usb or TV/toslink for tv/movies with this processor.
https://www.schiit.com/products/syn
When you're in half penny pinching mode and sound quality is the priority, you could try the new Sony STR-AZ5000ES (or go higher up). 2100USD. This is the first model where you get full preouts for your amps, not that you will absolutely need it. Sony's new 360 reality spatial mapping is a notch above anything i've heard in object based audio. They don't have a prepro with this new ES line yet, unfortunately.
https://www.crutchfield.com/p_158AZ5KES/Sony-ES-STR-AZ5000ES.html
Since you already have a Marantz 7706, might not be a bad idea to try something new. It is not going to be much of a revelation as you ascend higher on the Marantz chain (from what you already have).