Almost any GPS receiver made for the consumer market in the last ten years would work with this interface, if the receiver has an I/O port at all. Current GPS receivers made by Magellan and Garmin will function, as will almost all Trimble receivers. For the cleanest installation in a car the Garmin 16 seems to be a good choice at around $150. This receiver is a “smart antenna” with a single data/power cable terminated in an RJ-45 (I found a nice RJ-45 to DB-9 adapter at one of the local surplus stores that would do the job without requiring any fabrication at all). Here is a link to info on this receiver, http://www.garmin.com/products/gps16/index.html ; it can be powered from the Empeg serial connector (pin 4) and even receives WAAS differential GPS corrections for improved accuracy when they are available.

The hardware should be a piece of cake.

I would not expect the processing demand to be significant. There is no need to send data to the GPS. The receiver can be preconfigured to set the mapping datum and select the output data strings and should not require any maintenance. On the receive side the data are low speed ASCII strings, typically received once per second, that need a little parsing and perhaps some units conversion before writing to the display. I would expect this to be simpler than many if the visuals, as a processor task. I really don’t know how much spare bandwidth the Empeg processor has but I see it doing lots of other tasks like serving files and VNC clients and running complex visuals without affecting the music playback.