Hi Patrick,
I think you've answered the question...
QUOTE
All music equipment i.e. disco equipment, microphones etc. MUST be connected to the in-house sound system/speakers
Its their venue, and they set the rules. Don't break their rule - they can throw you out, and if they have a nois e ababtement order and your actions lost their entertainment licence, you could be open to damages.£££££
I have a wedding in a Maquee at the end of this month. The sound system looks to be a battered (and rusty) amp in a bashed flightcase.
Speakers are in a suspended ceiling directly above the dancefloor, with no other speakers.
I have explained my concerns to the client, and will be bringing a spare amp (the venue does not appear to have a spare).
In this situation, you have to realise that this is the clients choice/mistake. The venue obviously has had noise problems in the past, and so all performers are in this position.
For an 18th, I guess you may have wanted to bring subs/large powerful system - but now this is not possible.
On the plus side, you don't need to bring any PA gear, so your car/van and back will thank you
So.. don't sweat it, get in early (if you can) and find the limitations of the system - and try to make it sound nice (so don't pump up the bass too much!).
If they want higher levels, then you may be able to raise the mid eq a little.
Jason