The most I ever took in one sitting was the extracted amount from 2 8 ounce bottles of robotussin. The actual amount was probably around what you are planning on doing after adjusting for the efficiency of the extraction. I was completely incapacitated in that I would not have been able to even pretend like I understood what it meant to be asked "are you ok" let alone engage in anything remotely considered an activity of a developed species, that is to say make sure you have someone watching over you because you will not be able to do it yourself. Is it dangerous? Yes it is because of the amount you are taking you will be in a place where you can not fend for yourself or notice if anything bad is happening to you. I was with 3 other people at the time and was 17 but I made sure they knew what i was doing and how i would be unable to speak or "see" for a few hours.
Also make sure you are not eating or doing anything else that will interact with the dxm because at that dose your enzymes will not be able to metabolize anything else and you will be in danger of poisoning yourself with anything else in a sense. You are fine to do it just be sure you understand that this is not going to be "fun" in the classical sense, you will have an experience but it will be like a khole in a sense.
And If someone died on dxm it would likely be terrifying for them in its own right. Sure you can argue they wouldnt be able to fully comprehend what is happening but the in ability to understand a situation does not effect its ability to impact you. Odds are you incoherent self would "know" something was happening but you wouldnt be able to respond accordingly. There are few free rides where you are completely uninfluenced by your surroundings and I dont think a high dose of dxm will put you fully out.
