Remember what I was saying? Yeah.... http://slickdeals.net/f/8158166-500gb-samsung-850-evo-2-5-sata-iii-solid-state-drive-150-free-shipping
OH I GOT SO FUCKING NINJAED. DAMNIT
What @Killervolt put up is a solid build. The only thing is like I said the watercooler isn't my favorite. If you could pick up the Enermax Liqtech 240, which is a great AIO I would suggest that.
There's no real advantage that I know of for having two drives. I would also go with the suggestion for a different water cooler. I highly suggest checking out Jayztwocents for all of his watercooling videos as he goes over AIO's much more so than LinusTechTips.
My first thought is using Bluetooth. You could have it so that when the jukebox pi realizes it's connected to the Nas pi that it pulls from a certain directory you have setup (Ala music) and boom Shazam. Otherwise you hook ur phone up and you just play music through that also through Bluetooth.
With this idea both pis would need Bluetooth.
I have the xps 13. It is hands down the best laptop I have ever worked with. I hate apple as much as the next guy and I have no regrets about the xps. My suggestions though are, grab the non touch 8gb ram 128gb ssd. Replace the ssd with something bigger and you're good to go.