Roro,
Gl with the parlays no matter what you decide to do bud! Hopefully you get paid off well with the decision that you make.
Even at 87.5, I think the under is a very solid play and I'll give it one last shot for a large wager. I say one last shot because I don't see this series going to Game 7. Too many things will have to go wrong for SA to lose this game and a 10+ point win is likely IMO.
I know you asked me this question to give you a definitive answer as far as what you should do, but everyone is different with parlays and the risks they are willing to take. I think both sides that you have chosen are the right sides, but how much do you really want to risk to see if they both hit? Both teams struggle to put points on the board for significant periods of times so if you want me to tell you which play is more solid, its definitely the first half under because we can be almost certain (given what has happend the first five games) that at least one team will struggle. Now will that be the Nets? My best answer is probably, but it could be the Spurs instead.
Please let me know what you decide to do. . . I'll be rooting for you!