I guess its too late now but for future reference...You can plug your bass directly into the direct box. then you take another instrument cable and come form the Direct box to your bass amp head. This way, the sound tech can control your bass in the house and you can use your rig as your own monitor.
you could also take the XLR cable from the direct box and plug it to the DI out on your bass amp head. some heads have options like pre or post eq. unless your bass just sounds horrible, you probably want to set it to pre, which simply means that the house system will only receive the sound of your bass. There won't be any of your amp settings running through the house. If the bass needs some serious help with tone, you can set it to post and that way the house system will have the same mix that you have.
