I wish I could help, but I have never used an RSS feed! Hopefully someone will have a good suggestion. If so, let us know how it goes and if I should try it.
I've used and enjoyed both ReadKit and Reeder (my current one). I've never had any difficulties with marking items as read. I do not, however, use the Logos RSS feeds—it would be too overwhelming for me.
I use ReadKit and like it. Like Integ I don't use it for the Logos forums as (as far as I can see) you get everything from all the forums in the RSS feed and it gets too overwhelping.
I use DevonThink for this, as I make my notes in this program too.
As I have used many Bible programs, I am happy to have my notes in a separate program :-)
Hans
Maybe I'm missing something ... it's happened before.
Podcasts are RSS feeds and iTunes reads/subscribes to podcasts. Maybe iTunes is limited in some way?
https://rss.itunes.apple.com/
http://www.manythings.org/podcasts/how_to.html
http://en.wikipedia.org/wiki/RSS
http://itunes.rts.edu/rss.html (sample)
Is there a specific issue or something I'm not aware of with the RSS feed you want to subscribe? Maybe I'm thinking about audio and you have a text RSS feed. Does Mail handle that?
https://discussions.apple.com/thread/2690828
I just use Feedly since it's completely cross-platform. When Google dropped their reader, Feedly rescued a great way of keeping up with RSS feeds. Any browser, tablet, it's easy to have and access.
I too run feedly on Mac, Windows, iPhone, iPad. It runs everywhere, syncs everywhere.
If I remember correctly, Apple's Safari browser used to handle RSS feeds. Almost every browser now probably has at least one extension to do the job. FWIW, RSS is pretty much vanilla technology these days. Boils down to readability and access.