I've given up on the built in RSS functionality of the DMS. Instead I'm using the following:
http://www.ajaxdaddy.com/ajax-rssticker.html

you'll need a bit of background in HTML and java but for the most part you can google what you want to do, make the changes to the code, and call in your own rss feed.

On my test signs now I'm running our rss ticker, clock, and logo all on top of our background in one layer using java and html.
You can check it out here if you like: http://podcast.mclennan.edu/signage/background.html

Then i just lay my video content on top and it's good to go.

If i want to change the background or logo, i just overwrite the file "bg.jpg" or "logo.gif" on the server. The next time the page refreshes everything is changed for me.
No more need to log into dmm > add new asset > upload > start media designer > edit content > choose new image > save > send presentation to players (i think that is the condensed version)

(going to try it with images next!)

p.s. we are using 4305g and 4400 DMPs. firmware 5.2.2. DMM version 5.2.2.