So, to sum up the changes needed:
Ignore the bits about identi.ca, unless you want to use the service.
Use IFTTT to post to your FB page, Twitter, and Buffer from RSS feed(s). More functional than Twitterfeed at the moment.
Use idfromuser.org to find the RSS feed for your Twitter stream. (It won’t validate in most feed readers, but IFTTT can handle it.) This allows for (sort of) RTs.
This puts a bit more control in the hands of one service than I’d like, but it works. Keep in mind that some places (looking at you, Tumblr) update the RSS feed hours after the post appears.