Maybe, maybe not.

Are you connecting to the empeg with the laptop using the same cable?
Are you connecting to the empeg with the laptop via the sled connector?
Not enough info there to be sure.

The empeg sled connector is (in my opinion at least) wired incorrectly. TX and RX are set up to act as a DCE (like a modem) rather than a DTE (like a PC) but the rest of the serial port is wired as a DTE. BUT the serial port on the unit itself is wired like a DTE which means you need the null cable.

Soooo if you're using the same cables for both sled connection and direct empeg connection it won't work.

See also my post here:
http://empegbbs.com/ubbthreads.php/ubb/showthreaded/Number/116302/site_id/1#import

So effectively you need to use a null modem in all likely situations (i.e. PC direct to empeg unit and empeg sled direct to a device like your XM radio).

So as Mark says, check RX/TX

Always handy to have something like the picture for serial debugging. It's immediately obvious which signals are being driven. It's something I knocked up at my older employer since we did a lot of serial port interfacing. Can't seem to find anything similar online. For a once off it's not worth it but always good to have around.