Korg Poly800/EX800 Users

OK. so im not really an electronics guy.  but i did take a class in highschool and can am pretty good at figuring stuff out with a little help.  I forget how IC's are numbered.  what i can remember from highschool is that you start at the pin with the circle above it is ground or something.  so if anyone can give me a refresher about that....that would be cool. also.  I looked up on poly800text.txt like i was told and found that on IC1NMJ2069  sig1 and sig2 are DCO's 1 and 2 mixed in....does that mean that one of the sig's is ground. otherwise why would it be worded as mixed. 
 
what ive gathered is that i can put a input in place of pins 20 and 21 on IC1 but i'm sure which one is ground and if neither is ground then which pin is ground?  i know to someone with alot more electronics know how...these questions seem dumb and probably means i shouldnt be fucking around with my keyboard but thats why i have 4 of them.