I know this is an older thread, I just had this same issue today. I have an ampeg svt pro 3 which has a di, it is also part of a rack unit that includes a sonic maximizer, tuner, and compressor. I encountered this for the first time, where a sound guy refused to use my di, and instead placed one after my fx, and before my amp.. I was pretty annoyed, but gave in, after l having played for 20+ years and spending multiple hours perfecting my tone.. but then in the middle of the gig I went to tune imbetween songs, and realized I couldn't even mute my tuner. I don't get why a sound guy would be so against using my tone, when in 20 years I've nwver had this issue.