Best answer by Mathis
Hmm - not entirely sure how we can help with this if you're using a 3rd party service to have multiple RSS feeds actually. But let's see - I see your current profile image on SoundCloud is not 1400 x 1400 px - this is one of iTunes' requirements. Now, if the service you're using is pulling the artwork info from your SoundCloud account, then this would be reason a) why iTunes might not be accepting your feed(s). Uploading a bigger version of your profile artwork could fix this.
Other then that, iTunes has pretty elaborate documentation for podcasters here:
Maybe you'll find answers to your questions here? If not so, please let us know further details about your setup and what you're using for your feeds so we can look into this further,