Ya sounds like you might need a few accounts if you plan on keeping your revenue stream stable (one at a time of course). <<snipped>> I'm guessing you have a subscription model of some sort? Direct email marketing? If you contact myself or WHT posters please include as much information as possible about your business, starting with website, sales /marketing method and processing history (if any).
It should go without saying but perhaps for others who might see this post with less experience, INCLUDE EVERY DETAIL you can about this 'audit' and the 'invoice submitting process' you mentioned.
eBooks are not quite the welcome eCommerce 'hot' product the acquiring banks used to see them as in say 1998. I would also advise you confirm what countries you have citizenship in and potential Non-US based entities that you could use to apply for service. Ya, I'm not the guy who tells you what you want to hear just to get your money. That being said you also really might have just been unlucky with iPayment - and FD or some other real big company can have you processing by Tuesday ;-)