Congrats on the new car and welcome to 6mt.
The unit from everythingg35.com is the only interface that allows you to have ipod and OEM satellite connectivity and control both from your radio AND keep the steering wheel controls. I have one in my sedan. you just have to disconnect the iPod to listen to satellite radio.
everythingg35.com is also a great place to get the sat tuner. Both the tuner and the ipod adapter are easy to install yourself.
As for adding a sub, that is fairly simple with the Bose system. Look in the audio section at g35driver.com.
4080 Enclosures has nice sub enclosures that look like they came from the factory.
