Fwiw you can post to both Lemmy communities and Mastodon at the same time, that does work pretty well, but it has to be from your Mastodon account and you tag the Lemmy community as a user. (First line of the Mastodon toot becomes the post title on Lemmy, fyi if you’re going to try it, and you can tag the community at the end it doesn’t need to be the first thing in your toot)
Not actually sure if that works the same way for Kbin magazines, I’m subscribed to plenty of them but most of them are kind of inactive so never had chance to test it. If anyone’s done the science and can report back, that would be interesting to know!