Wow pretty ambitious system for a "Newbie"!! Mac is great and you have synergy if you keep your amp, Lexicon is a great piece for HT also look at Anthem. What size is your room? (with a 7 channel amp you could go 7.1 if your room is medium/large to a large room). I would also put some serious thought about budget and stick to it (good cables and interconnects for HT snow ball fast)
Good luck in your search!
Good luck in your search!