We'd like to share the sales with our author, but there doesn't seem to be a way to do that with KDP and I'm wondering if maybe there is another/more-appropriate-account-for-us/etc way for us to publish e-books. I found info about "Amazon Seller" accounts (http://www.amazonservices.com/content/sell-on-amazon.htm#!how-it-works), but they seem to be more oriented towards physical products than Kindle e-books.
Is there a type of account that fits for publishers that don't sell physical books, but are bigger than single individuals?
You as the publisher are responsible for sending monthly sales reports to your individual authors along with any payments owed. Amazon is a distributor only. It's not their job to do that for you. That's why they only offer the one account.