AOII and HiLo are different systems
AOII (Advanced Omega II) is described in Bryce Carlson's Blackjack for Blood, while HiLo is described in many texts, particularly Standford Wong's Professional Blackjack.
Both AOII and HiLo are balanced counts. HiLo is a level 1 count (so all the card tags are -1, 0, and 1). AOII is a more complex count system: first, it's a level 2 count (so all the card tags are -2, -1, 0, 1, and 2); and second, it requires a side count of aces for maximum effect.
If you'd like more information about these systems, both of the above-mentioned books are available from this website.