As Josh said, they are all DCC ready. It is very easy to replace the Athearn board with a decoder board. TCS even has a decoder with built in resistors so you don't have to change the bulbs.
http://www.tcsdcc.com/decoder/A6X.htm
$90 for a RTR Genesis is a good price, but if it is really old stock that you have to put all the details on yourself, not such a great deal.