RE: Just bought a slow stix and a Spectrum Dx6i and having trouble
Assuming that your LHS plugged the servos into the correct Rx connectors you need to bind the Tx with the Rx. Your radio came with a combination bind plug. Combination? Yea, it has 2 adapters. One is a male connector - just like the connector on a servo wire - with a short wire loop connecting the outer 2 pins. The other is a female connector that would accept the male connector. The male connector is intended to be inserted into an open channel on your Rx. The female connector is used when you have an external 3-wire charge port. In your case, use the male connector.
Follow the manual instructions on page 18 to bind.
Btw - some add a 3" extension wire to an open channel and leave it accessible so that they can bundle up the Rx for protection yet have easy access to the Rx using the extension to re-bind.