Just 2 excercises for Back ?
If you think about it...... your back consists of how many muscles ...... and you give the same amount of sets to your biceps which are how many muscles ??
So if you come to the conclusion i did, you would figure your back needs ALOT more work than biceps !
There is over 30-40 excercises for your back.... choose more.
Also in regards to doing Back-Biceps if i were you i would reconsider it.....
Doing your Back also uses your Biceps... so when or if you follow my suggestion you will find your Biceps are pretty fried after your Back so maybe swap them with your Triceps....
Like a good split would be:
Monday: Chest and Biceps (As the Triceps get used with Chest)
Thursday: Back and Triceps (As Biceps get used with Back)
Followed that for many a year
But of course, its up to you.