Joining Accounts Possible?

You can't merge two accounts, but you can make it so that your original account with your microtransactions can be played on Steam. However, if you already have an account with Steam that you don't want to lose you'll have to un-link it from Steam before you can begin. To un-link from Steam, please contact support@grindinggear.com

However, if you want to link an account to Steam you can do this by logging into your account on the website and going to My Account, Manage Account, Steam and follow the instructions here.