Looking for recommendations on osCommerce-accounting software integration

Hi there folks (I'm new here).

I've got a question for my fellow e-commerce developers...

My client and I are currently trying to figure out the best accounting system to use for their needs. They want to automate as much as possible using the data in osCommerce (the shopping cart). In particular, they want to be able to:

i. Pay the manufacturers
ii. Have the manufacturer send them bills
iii. Do the accounting

To clarify the terms, their primary supply method is drop-shipping. They receive orders from customers, in turn place orders with their manufacturers, and manage the shipping process using contractors or directly. They need to be able to track all these transactions and take care of their billing as well. Right now, it seems they mostly want one-way osCommerce -> accounting.

They're trying QuickBooks Online at the moment and asked me to integrate it with the site, but honestly, the options seem few, and we don't have the time to create something from the ground up. I've been looking a lot at eCC, but I don't know if it works with QuickBooks Online.

In any case, something that can perform these functions (or perform them with a few hours customization) would be great...

I hope I've described the scenario accurately enough. If anyone has any ideas at all or pointers in the right direction, let me know!

It's worth mentioning they have a soft spot for QuickBooks at the moment. They weren't too hot on FreshBooks.

Thanks in advance,
Kevin