I do believe the 7702 and 7009 are equal in terms of sound quality. I have the higher end 8801 and I find it equal to my previous Denon AVR-4308 in pure direct but the sound processing of the much older Denon was not as good.
The 7702's RCA is also rated 1.2V. The 2.4V rating is only for the balanced outputs, the 7702's unbalanced outputs are rated the same as the 7009. In fact, pretty much all Marantz (including their flag ship AV8802) and Denon AVRs and pre pros are rated 1.2V for their unbalanced (RCA) pre outs. Every single bench tests, including those done right here at the Audioholics, found their maximum unclipped pre out outputs exceeded 2 or even 3V by a wide margin, so that is not a factor at all for most power amps that have typical gains of 28 dB or higher.
Here is a link to the AH (by Gene) review of the X5200W, I expect the 4200 will not be far behind.
https://www.audioholics.com/av-receiver-reviews/denon-avr-x5200w/measurements
Quote:
"The AVR-X5200W has plenty of grunt via the preamp outputs to use in conjunction with virtually any separate amplifier should you desire more power. I measured unclipped output of 4.5Vrms from every channel. We like to see at least 2Vrms and the Denon met this with over 6db of margin to spare."
Note that the 5200 is also rated 1.2V. I am not sure why D&M rate their pre out output, Yamaha's appear to be even more conservative, IIRC they rate theirs 1V. I suspect they may base it on the voltage required to drive their internal amps to their rated output, but I am not really sure. All I know is that bench tests by AH, S&V, HTM, HCC, AVtech, all showed much higher measured output voltages on their bench.