Just Use The Google Reader Feed
I found that my Google Reader account automatically sums all feeds into one big feed. I can easily add that to apple mail.
In Safari, just look for the little RSS icon at the end of the url in the address bar when you're on the Home page of your Google Reader account. Click on that RSS button.
Copy the resulting string and load it as a new feed into Apple Mail. Before you submit it change the prefix to the url from "feed://" to "http://" - without the quotes - and you'll be all set. You might even be able to single out the feeds and import them one by one if you want, I didn't care to try that.