Hey hey,
I bought the white Super 8 about a week and a half ago. I figure this will be a better place to discuss the system with you outside of ebay's restrictive character limit.
I tried linking the audio channels with two 10ohm resistors in series, and then ran one wire to the AV port and then bridged it again between the left and right audio pins under the SCART hood. This didn't work out very well at all, low audio that was very buzzy, however I bridged the channels by linking the phono jacks with resistors; maybe that is unoptimal.
So I undid all that and went back to how I was running it for the first week, which is as follows: It just so happened that the model 1 genesis SCART cable that I had free linked the mono channel across the left and right in the SCART hood. It then paralleled that split channel into a stereo phono jack breakout cable. So what was intended to be used as a Genesis audio output, I was using as a NES audio input, with the bonus that it mixed the channels together, which is what I wanted.
I was only trying to get the audio out of the Super 8's AV port because my SCART's audio breakout cord was too short; so i just put a longer one in it and all is well.
Something I have noticed is that unless the two phono jacks are hooked up the video brightness is significantly reduced. I love how bright the output is on my CRT, so much brighter than my other RGB NES.
But why the picture is only that bright with the audio hooked up does concern me. I am primarily concerned about a difference in power being fed to the PPU with the audio jacks hooked up then not. I am a layman so I can't begin to dechiper or second guess your PCB, and I have no evidence that there is anything to worry about at all, but given the age and rarity of these PPU's I'm sure you will forgive the inquiry.
The Super 8 has been fantastic so far. Sharp output, very bright, and loud audio. I have seen no glitches of any kind in the games i have tried on it, including a non-Mike Tyson Punchout.
The only place that I feel the Super 8 doesn't beat my other RGB NES is in sound quality. The other unit used a particular audio amp of some kind and while the audio is separated, it is quite punchy. The Super 8's audio is nice and loud, but sounds a bit tinny in comparison. But it is still loud and clear, much better than a stock NES, and with my current cable configuration it has much less audio buzz than is average for my old RGB systems.
Regarding your proposed alternate AV pinout. No Genesis SCART cable that I have purchased has ever carried the top right pin, and if it did, then I don't know where it would terminate in the SCART hood because pin 21 would already be taken by composite video. I know of a seller who does sell genesis SCART cables that carry the top right pin, but they would terminate that pin on 21 again for sync.