Hello. The Pandora issue can't really be worked around. It's configured to time out. If you have an AppleTV, you can send the audio from iTunes or from your iPhone.Another option involves getting a sound utility like AirFoil or something similar. These utilities can send audio from any source on your Mac, not just iTunes.
To control audio coming from your Mac, with your iPhone, you'd only need an app called Remote. It's made by Apple, and it's free. You can pair the app with your iTunes library, and browse playlists, change tracks, change volume.
If you have multiple speaker setups or rooms, you can use an AirPort Express in those rooms and give them each a name (Living Room, Study, Patio, etc.) and select the destination for the audio from iTunes.
Could you please give me a call at (XXX) XXX-XXXX. I would like your thoughts re the brand of speakers to buy. I understand that Bang & Olufson has a good product.