Hi Olly,
if you (or other DJs) are the only one playing from the Twitch, you should not have an issue. You can adjust the PA or AMPs according the loudness you need, just don’t hit the reds (!).
If you are performing after another DJ with CDJs, powdered controller, mixer orso, you might find that your sound will be less loud, especially when the previous DJ was working at the limits of the PA.
A good way to add some ‘bite’ to your sound would be to connect both master and booth (oh, set the booth output switch at the back to ‘main’ first) to the in house mixer. You will add some dBs in loudness. You could also buy a small line AMP that adds 2-3 dB to your line level, before going to the in house mixer. The latter will leave your booth output free.
regards,
King of Snake