Disklavier

I have a new DC3A arriving this week :) and will be connecting it to 
my synthesizer.  I have all the midi cables, but what kind of 
connections does the DC3A control unit have to the Aux in and out?  
1/4", RCA, ??  Also, can I feed my synth into the Aux In and have it 
play through the DC3A speakers?  Does the internal DC3A XG/GM sounds 
still play when you have something coming into the Aux in?  Or do I 
have to use the Aux out (mix it with the synth) and then input it 
back into the DC3A (Aux in)?  Hope this all makes sense.  Thank you!