@elliottbnewcombjr
"Nd9 is not compatible with non-Rega tonearms due to its 3-point mounting system"
This absolutely is not true, the only difference is the locating screw ahead of the conventional cartridge mounting screws, all you have to do is align it like you would any other cartridge. Their cartridges will work with any arm that accommodates VTA adjustment and Rega's cartridge height dimensions. I believe all Rega cartridges weigh 6 grams.
https://www.rega.co.uk/
https://www.rega.co.uk/products/planar-8
"Anyone know the channel separation and channel balance specs of Rega Cartridges? Post a link please. Thanks"
I doubt any of the following will give you what you’re looking for regarding Rega cartridge specs because I think they’re deliberately vague on the subject as they are with all their products specs. I did provide the direct link to their site so you can peruse it yourself. The rest of the links are to the English publications of The Ear and AV Forum.
https://the-ear.net/news/rega-nd3-neodymium-moving-magnet/
https://the-ear.net/review-hardware/rega-nd3-redefines-budget-mm-cartridge/
https://the-ear.net/review-hardware/rega-nd5-moves-the-mm-goal-posts/
https://the-ear.net/news/nd7-the-ultimate-rega-mm-cartridge/
https://the-ear.net/review-hardware/rega-nd7-takes-on-the-best-in-class/
https://the-ear.net/news/rega-nd9-boron-cantilever-mm-shocker/
https://the-ear.net/review-hardware/rega-nd9-the-accidental-masterpiece/
https://www.avforums.com/reviews/rega-nd7-moving-magnet-cartridge-review.22088/