Discipline ideas for 6 year old boy

We don't spank, never have. I honestly don't think it would work anyway. Our 6 year old son loves watching YouTube, his favorites are Danny Go and Number Blocks. He doesn't watch an excessive amount of TV, but we feel like taking away TV is our only "weapon" as time outs don't work. We call it his calm down corner. He utilizes it when he wants to. He is ADHD combined severe and also diagnosed with anxiety and let me tell y'all we are at our wits end. My poor husband is desperation will threaten to take away TV for the next day and my son just comes undone. He will ask over and over and over "Do I get TV tomorrow?" While screaming crying and begging it's absolutely horrible. I have decided if we can't take away the TV right at that moment, then we can't threaten for the next day etc because he just absolutely loses it and will constantly worry and ask about it. It's hard to differentiate anxiety behaviors vs adhd at times. He obviously needs some form of consequence. We are absolutely clueless as to what to do. I should mention he's on Vyvanse, and likely still adjusting to a dose increase. We want so badly to do right by him.