In short, anything is possible, especially if it’s written in 0’s and 1’s… I know this kind of answer does not help you much
What I would do is switch completely to Magento. Why? Well, you have a working site for now. So leave it working, while developing completely new one aside, since the message I read does not strike me as one of those “it must be done yesterday”. Why I recommend switching fully to Magento?
Magento is powerful, really powerful… it will get even more powerful in time. Community is growing up in numbers each and every day. It’s future certainly seems bright.
So my question for you is: Why would you make mixed system with limited capabilities of one and other when you can have full potential of the better one? The thing you ask can most certainly be done, but why? It will only take more time to develop, maintain and most important updates… Things sometimes break after updates… Why risk hunting bugs in mixed system? What happens when you wish to hire some other development team? They’ll have to spend some time connecting dots between those two system. Time you will have to pay.
It seems easier to write some custom script to do export of products into the Magento system then to combine them to work together. Once on Magento, you only need to take care of one system.
Switching to Magento would require
- custom script to export import products and all relevant data from old system to Magento (not sure on time, never done it )
- setting up the payment and shipping methods (could be done in under 8 hours… just set up options in the admin interface and test them)
- additional testing off entire system (wish list, add to cart, compare products, product images… I mean everything) (under 8hours...)
you would need to test it good since you imported product, just in case something is not broken
- switching current theme to Magento (could be done in a 16-32hours, I just hate styling )
Most time consuming would be the first on the list, custom script…
These are just my thoughts. Not sure if it helps you…
Wish you all the best.