Confusion with mixer routing? can any one help please?

[c_r_a_z_y]

Can any one help!
Im bought Behringer 1604 eurorack the other day and its routing has got me stumped! I was just about to do some work with my comp then realised I wouldnt work out how to route my mixer to do so!
Can any one help me out and tell me how please?
I use the minjack on the side of my iMac to record in from my mixer and then out of the headfones socket into my mixer.
I use the tape in and out to put these in to.
Then I send the signal out to my studio monitors through my main out.
I plug my guitar pre-amp into one of the inputs.
what I cant work out on the behringer is how i route it so the signal from the guitar goes to the computer and then I can just hear the out put from the mixer.
At the moment I can only get both of them together and alot of feed back and stupid noises! can any one help me please Im very stuck!
Thank u
craze

 

[TexRoadkill]

Use the main outs or the channel insert to send to your Imac. There should be a monitor switch to activate tape playback monitor so you can mute it when you dont want it. If that is not the case than run the out of imac into a channel onto the mixer and mute it when you dont want it. Use the monitor or control room output to feed your speakers.