Nah, I'm with
@saabfender on this one - give up the fight. Why do you want your cab to be mic'd? Are you running an overdrive pedal that sounds harsh when DI'd or do you just want to make sure the audience hears your SVT cab? If it is the latter, I'd say you're causing more trouble than its worth. No one in the audience cares what your 810 sounds like. I know that sounds harsh, but it is totally true. Send the DI line from the back of the amp and that should be enough to preserve your tone.
I mic my cab and DI, but that is because I treat my DI line as a "dry" line and my mic as a "wet" for my pedalboard. When I don't gig with my originals band and don't have all the crazy effects (doing cover gigs or sub work) I don't even bring an amp half the time. I talk to people in the crowd all the time who didn't even notice there wasn't a bass amp onstage.
This is the worst advice. If you quarrel with the FOH, you are always going to come up the loser. You are completely at his mercy. if you try some ultimatum crap on him, chances are he will tank your sound live. Why wouldn't he? It's not like he has a boss sitting there waiting to give him grief cuz the bass guitar was mixed so low you couldn't hear it, or was all boom and no definition, etc.
Think of it this way: imagine if you worked in a big box type store and a customer told you he did not want you to use a hand truck to move a heavy item because he thinks it will damage the item. You explain to him that the item is in a cardboard box and has packing foam inside that box and that there is no need to worry, but he is dead set on making your job harder anyway. How would that make you feel? Would you want to offer that guy great service? I wouldn't.
Maybe instead approach the sound guy like this:
"Hey, my name is _____ and I'm the bassist. Do you plan on running a DI for the bass amp? I ask because I always bring this Make/Model mic with me I like to use.
What do you think, mic or DI? I personally prefer the mic
but its your call."
I know we all think support staff at events are there to cater to our artistic vision, but that's just a fairy tale. These guys and girls are just at work, doing their job. They probably would rather be somewhere else - maybe on stage with their bands instead of doing a thankless job where they constantly deal with amateurs who think they know better than them.
The irony of this is that my own set up in my originals band requires a mic and a DI, but I just explain my set up to them and ask for what I want in a way that frames it like it is beneficial to them ("If I could have a DI for my dry side and a mic on the cab to send you my effects, then
you can mix to taste out front.") It never fails.