The best solution might be to hire a programmer (either a free-lancer or a software programming company) to write a program that synchronises the database of the webshop with the database you use to maintain your products (SKU's) and stock for each SKU (not to forget the price and where you buy them). After all, you don't want to offer a blue XL version of something if it doesn't exist or is currently out of stock, so both your SKU's and their availability should be in the database of your webshop.
Then you can keep your current store (both the database, the front-end and the back-end). It's just another way to fill the database.
I am looking for a shopping cart for e-commerce that allows you to bulk upload attributes (size, color, etc). Most of the carts I am finding require the product option or attribute to be installed and then attached to the item. I have over 10,000 items and each color, size, and feature varies by brand - it would take forever to create applicable product options or attributes within the system (trust me - I have already done it with Zulu Cart). Any suggestions? I also want to keep my store front. In general - I would want to up-root from one location and plop down in another within a disruption in business.