Hi Subzero,
The RSS feed in the Firetank Feed Manager for x-cart is supposed to operate like that, it's for listing the newest products on your site on other RSS enabled channels. If you require it to show all products it's a case of altering the number in the class file for this, although keep in mind most RSS channels will not accept large lists.
If you need extra information or help on this please email us directly on
http://www.firetanksoftware.com via the links on the contact us.