I upgraded mine with kit and info found on this website:
http://projects.gbdt.com.au/eq6-1/
After this upgrade, standard EQ6 has serial port (LX200 goto and guiding) plus some other improvements.
The upgrade is very simple to do, and it may be free, if you know how to use soldering iron and if you know how to program Atmel processor, used in the mount (
http://projects.gbdt.com.au/eq6-old/).
I purchased the kit because the whole job is cleaner, and the rework is reversible this way (not really important in my case).
Also, this mod leaves the space for later stepper motor replacement, as the gear ratio is programmable via serial port.
At the moment, I am happy with the tracking and periodic error (it is smaller than 15 arcsec, I reckon).