It worked and So I come back to Mars Edit to see if I can do something similar to get a Podcast into a post from a url. You can click on Media and do an upload to the blog of your media. But what I wanted is to continue using Libsyn because I like the stats from Libsyn.
So same as with Blogo you have to go to the menu Post and click on Edit Enclosure. In the dialog that comes up you can paste in the url and even cick on a button that will fetch the type and the length of the podcast in bytes from the url.
For the fact that MarsEdit has the box ready to past in the url and that fetch details functionality it gets the nod on that side of the job.
I am still waiting to find out if Marsedit can post to Ping.fm. I use that a lot and it is a deal breaker for me. I have the paid version of Blogo and I like its ease of use and the Ping thing. Will not pay out extra money for MarEdit when Blogo does all but is a little more fiddly for some things.