Sorry about your RX-Z7, but you misunderstood the preout specs.
It is true that some AVR, such as some of the lower Yamaha models, have lower output than Denon/Marantz, but you can't just go by the spec'ed 1 V without knowing the conditions. Take a look of the higher end units and you may find in some cases they provide more information than just 1 V. That 1 V could simply mean at that voltage, an amp with the same sensitivity as the RX-Z7 will give you the same output (as the RX-Z7),or it simply means 1 V at a certain load impedance, such as 470 ohm for Yamaha's at a given THD.
Bench tests after bench tests, including Gene's on Audioholics.com, have shown that AVRs with 1-1.2 V specs managed to achieve above 2 V cleanly. The same apply to prepro and preamps, below are just a few examples:
Marantz AV8805 - $4,500, preout 1.2 V
Reotel RSP-1582 - $3,500, preout 1.0 V
Yamaha - CX-A5100 - 1.0 V/470 ohm, 4.0 V or more maximum (0.06% THD)
I am not trying to contradict you in anyway but simply want to point out the fact that the 1.0 V period kind of spec does not tell the whole story.
Another thing, if your prepro's preout is specified 2.4 V XLR, it it still just 1.2 V RCA and you obvious know that and for short distance of 6-12 ft, you are not going to notice any difference in SN, in fact most S&V bench tests show RCA did a little better.
By the way, you mentioned the 9B, that's a lot of money for less power, compared to the Monolith 200X5.