Thanks so much for the initial responses. The HKG website suggests that TG is one of the airlines that offer early check, so will definitely check the transfer desk.
Regarding about staying in downtown, it's not completely out of the planning yet. However, I thought the overnight package at the lounge in HKG (11pm-7am) is the better option for my schedule. Arrive 6 pm in HKG, then head straight to downtown for some sightseeing and then head back to HKG taking one of the last trains, get some sleep and I should be ready for the early 8 am flight to MNL. In whichever case though, I sure hope I could obtain the boarding pass with my TG flight upon arrival.