If you want to boost for this you can get 8 in a row easily with akuma on the first survival challenge. You have full ultra and super combo meters from the start and they stay that way the entire time so basically you can just keep super attacking.
Pick Akuma(or if you dont want to wait until you unlock him any other character whose super combo you can do well), I use Akuma because his ultra is easy to do. Low Punch, Low Punch, Backwards, Low Kick, High Punch. Right off the start do the ultra and that should take away half of their health, then while they are getting up do the ultra again and they should be dead along with an ultra combo finish. Some characters require 3 ultras to kill them but its not that hard with akuma to finish them off with a super or ultra. You can also boost the super and ultra combo finishes this way.
You could also go into versus mode and use two controllers, Beat on the second controller character until you get your super meter full and then if they are low enough do your super combo and finish them that way. Or beat on your account with the second controller until the revenge meter fills, then with your account hit the second player until they are low enough to be killed by an ultra then do your ultra. This would take more time but you can maybe get more in a row this way, if you are having trouble with the survial mode technique.