Jday bosses use tremor, its magic damage spell that will reduce your hp by %, so you will take lot of damage, thats unavoidable.
The way to to jday, if you read the guide about this quest is about isolating the right boss there (one with heavy armor looks different than others). Do this by running from tp, kiting other ones into far side of the map and tping out or dying. There is more of these guys now than in previous patch, but strategy is the same.
You start the actual fight when you are in some corner of the map 1v1 vs the boss, then you will take damage from time to time from his tremor. Do not try to spawn killable bosses before you are 1v1 vs correct guy, it is crucial for success with this build. If you were a summoner you can handle all of the,, but not this build.
Once he spawns boss to kill, surrounded by edyrems, you should have massive stack of fortress ready to snipe that boss (you should cast fortress + edyrems all the time), and as soon as he appears, smack it with iceburst. With t6 gear and just the charms listed in the guide that you should have at that point of time, this deletes that boss in literally 2-3 seconds before he can summon anything (if they live too long they cast their spells or summon more invicible barbs, which makes continuing the fight in order to summon 2nd boss way harder).
As for survivability issues, I don't know, if you don't run, have those stats, you shouldn't have problems.
In Toraja you are supposed to fight just maximum of several amazons at any given point of time. Use thunderslam, rely on thundergod novas, kite back, if you aggro too many of them. It is very easy to overextend in that area. Not only you start to take too much damage, but also it is impossible to summon enough edyrems, because they die immediately as you summon them. But if you utilize aoe stun and fight limited amount of those amazons, you can handle them and clear the entire level with enough time.
Kabraxis is more difficult, it is pretty far on the list so dont approach unless you have nice collection of charms. Your defense later goes up to over 1mil with 2h axe.
Some ppl asked about lategame gear suggestions, I recently found that tundra set fits that role pretty well, this set is godly.