Sure, you can chain as many mixers as is needed to create a suitable composite signal, and that trick works for either audio or CVs. Just don't make the mistake of trying to sum the outputs via a multiple, because that would be about when you'd discover that your outputs didn't have reverse protection (resulting in a rather expensive POP!)! Also, you can't exactly use a mixer to sum gates and/or triggers; this is best done with some module that doesn't have a possibility of attenuation, such as a Diode OR or something similar.