I have a 100 smithing and I've been able to improve my ancient shrouded armor to Epic. Just wondering if its possible to raise to legendary or not? I've tried drinking a couple of fortify smithing potions along with a blacksmith potion and it still doesn't give me the option to raise it further. Thanks in advance for the help.

Yes it is quite possible. Try buying some fortify smithing gear at a merchant shop and using that in conjunction with the potions.

Okay so I tried with some gauntlets of major smithing (17%), 2 potions of Blacksmithing, and 2 fortify smithing potions. Still can't raise it. I must have to boost by several hundreds of percent. The blacksmith potions raise it by 50% each and my fortify smithing potions raise it by 46% each. Does anyone know the exact percentage you need by chance?

Yes, I know almost exactly the percent.
You must think you need something near lvl 200 in smithing. That's +100% bonus to Blacksmithing I think. That's the only way to turn th Ancient DB armor to legendary. I could only make it flawless.

Quite impossible without hard potion+enchanting or Cheats.

You must improve ARMOR + GAUNTLETS + NECKLACE + RING + POTION to get legendary.

You can only have the benefit of one blacksmith potion at a time, so you'll have to find a ring, necklace, chestpiece and bracers with fortify smithing, or enchant those yourself.

There's also degrees of legendary. If you boost your smithing to the 200s, the armor and weapon types that you have perked (glass, daedric etc) will be much more powerful than when "merely" improved at 100 skill level.

Oh ok. So my fortify smithing potions don't stack either? Or are you only referring to the Blacksmith Elixer?

Nope, potions that gives the same effect don't stack.