The sound man says the signal level at the console trim pot is too hot. The pot needs to be set at about 8 oclock...
May I ask why it needs to be set at 8? In my experience as a soundman, I often leave the trim pots - also known as channel gain - at zero. The trim is just another preamp on the line - if the signal is hot enough to not need it, turn it the hell off!
Now, if the signal coming into the board is so hot that it
still clips, even with the trim at 0,
then you have to look at alternatives. Generally, turning down the source is more than enough.
Is the line out of your amp a DI out - i.e. an XLR low-impedance balanced - or an actual 1/4" TS line-level out? If it's the latter, you have two options: either tell the soundguy to jack you into a line-level input, or stop using it and plug into the board through a DI. If the former, then you'll have to turn it down. If it doesn't have a dedicated level control, you'll just have to turn down your amp or bass.
...and yeah, an attenuator
would do the trick, but is completely unneccessary.