Too bad, but fortunately the effects of poor measured performance by ASR, AH and others have started to to influence the manufacturers. If there was not time to get the SR8015's upgrades to the 7706, I have a feeling we will see it in the 7707. The lower cost 770x line are upgraded yearly while the TOTL 880x's don't get addressed till at least every 2 years. Maybe they want to wait for the next 880x to get it first, wouldn't want the 7706 outperforming the current 8805
I think cost may have played a big part. The AV7706 has the balanced circuit so it will need twice as much HDAM modules as the SR8015 assuming they have the same number of channels. So Marantz may have opted to use their better version in their flag ship AVR, AVP and integrated amps only. The AV7706 is basically derived from the SR7015, but add multichannel analog inputs, XLR outputs, and subtract the power amp section, and replaced the much large power supply with a smaller one.
One funny fact by the way, my AV7005 had a 100% toroidal looking PS transformer but the info sheet indicated that it was toroidal, so I contacted Marantz support and they confirmed it was just an E-I transformer, but encased by a toroidal case. I wasn't upset because I do not it is not true that toroids are always/automatically better, it often is, but it depends. It just show there has always been a big gap between the build quality of the 7000 and 8000 series preamp/processors, though the key parts and circuitry are the same, including the HDAM modules, until now (i.e. the SR8015).