1. you do not need a "Y" splitter, you already have to sub pre-outs on the receiver. The "wake up" is when enough audio signal goes to the powered sub, the amplifier switchs out of standby to full "on".
2. Definately bridge the red-red and black-black binding posts on the Monitor 70's and use a single 2 conductor speaker cable to each Monitor 70
3. Why ? Elemental Designs know exactly how to design a great powered subwoofer, why mess with it.
4. The sub will respond to the gain setting in the a/v receiver setup (a variable set in the setup menu) and the gain of it's own internal amplifier - experiment
5. The first thing you should do is listen to the system in it's "default mode" so you will have something to compare the audyssey choices and settings against. They do not always sound right the first, second or third time you run the program.
6. Yes, with a powered sub, speakers to small, subwoofer present (and I think you choose the LFE Plus setting so the sub will work with all audio input, not just the LFE channel stuff). Others will be far more knowledgable here !