If you have the 128 memory expansion and your song is not to long and don,t have the entire memory loaded with samples. You could convert the entire song to 1 sequence and record it on the record page with "input" set to "main out". Then save the file to harddisk or memorycard and then you can send it to your pc the way you wan,t.
(you can,t record while in song mode, but you can in pattern mode. So that,s why to convert the whole song to 1 sequence)
But it would be more likely that the memory in the mpc comes to short, so then you have to record its digital or analoge outputs with another device.
Then i would say record its digital output, cause then you don,t have quality loose due to unnessecary DA-AD converting