Hello Luis,
Yes, as Martin pointed out, with the current number of amps you have you have the possibility of 4 separate audio channels, and as Joe points out you might come across a home theater amp that has discreet inputs and outputs although they are not very common.
The biggest thing as Martin pointed out is the audio interface, you will need that first. Once you have that it opens up the possibilities as you are currently limited to 2 channels and you also have no possibility of rank routing options. With the proper interface you then have control over individual ranks of pipes or even entire divisions of pipes where it allows you to choose which ranks or divisions you want to go to which speakers, something you can not currently do now and is what can really make a big difference in the sound. If it were me, I'd be shopping for an interface capable of 8 to 10 channels of audio, then you can add more amps as time goes on or purchase a single multi-channel (discreet inputs and outputs) amp, and of course more speakers too!
Marc