First of all, thank you for your reply.
I have one question regarding a previous setup that I had. I originally had an active Di Box (https://www.storedj.com.au/behringer-ultra-di-di20-2-channel-di-box-splitter) running out from the acoustic guitar (with a built in preamp) and then into front of house. It produced a large hiss noise, and I wondered where this was coming from. I then tried plugging the electric keyboard into the active DI and the same result was present. I then concluded that the Di box was broken. Would the hiss have occurred because I did not use a passive Di box instead of the active, because both instruments had built in preamps?
Robert is right - your DI is very low-quality and/or broken; it's not an active vs. passive thing.
Generally speaking, active DI boxes were designed for very low-level devices like passive guitar pickups because their extremely high input impedance won't load the guitar pickup down which could affect the guitar tone. That said, a quality active DI can take a very high level as well. If I remember correctly, one of the first active DI boxes - the Countryman 85 - boasted that it could take a 120v mains level signal without damage.
If necessary, the pad switch is there to knock down really hot signals.
Get a good active DI and you will be fine. The Radial Pro48 is a great choice at a reasonable cost, as is the BSS mentioned, however I prefer the Radial as the BSS effectively has an off switch that is problematic.