I just saw this post and even though it may be too late, somebody else may find useful to know that it is possible to set whatever you want to display in the homepage (this includes the two slideshows and right/left column).
However, as far as I know this is only possible through categories and not for individual posts. This means that you have to create a specific category to be either included or excluded in the slideshows you want.
In this case, if you want to display only posts with an image, as kitcorsa asks in this post, you need to create a category for posts with images (Yes, all posts with images you want to be displayed in the slideshow must have this category). Then you go to the myMag Theme Settings Page (In your Dashboard right menu, under appearance click myMag Options and under the Homepage Settings look for the slideshow you want and enter the category ID number of the category that has all your posts/articles with images.
Or alternatively, you can also create a category for posts with no images and under the Homepage Settings enter the category ID you want to exclude (which is the category of posts with no images). The Recent News Category ID box is where you edit the posts at the news feeds to the left/right column (mine is at the right).
How to find the category ID number?
Under Posts at the left menu of your dashboard is the Categories option. Once there you will find all your categories and click on the one you need to see the category ID. You will find the number in the URL in the address bar of your browser. Or just do it like me, hover on the pointer on the category without clicking and (depending on your browser) you will see at the bottom the link address without opening the website. In this link address is the Category ID.
Use your own creativity and “Math” to make combinations of featured posts. I personally didn’t like to see the same images in the two slideshows, so I changed the categories to be displayed in both. If you know something different and easier, let me know.