I just make noise with two mixers and I'm always turning volumes down because I'm afraid of not only blowing my speakers but sounding flat too. sometimes you might want to sound flat, ok, if you play with distortion a little bit you might find "interesting" flat sounds aswell. Basically, more mixers the better - than you need to feed them and you have just more options than you need (computer, cellphone/tablet, contact mic wtv) if you don't have more than one source just split it, go diy.
You can do everything in some daw like ableton or something but it's just like drawing in the computer with the mouse instead of having the paper and the pencil ahah
Btw, someone here have some advice about how to play real loud with some safety for the speakers? I just blown one 4 or 5 years ago... I didn't had a proper mixer tho