Best computer for usb hi fi source

Auralic Eries
Alan

Any of them can be made to sound good. However, IMO, Macs are the most natural choice for music. I use a Mac Mini of the series right before this latest release. The caveat with the new mini is you cannot upgrade the RAM. Also, the processors are duo core instead of quad core Intel's.
The MacBook Pro would be my second choice but the IMac is decent too.
I personally use a mini with a quad core I7, 8 GB of RAM and a 516 GB SSD. I also use Pure Music 2 with an outboard drive to store music on. iTunes is strictly a library file using the Apple Remote app with an IPad. Works beautifully, sounds great. Only time things go south is when the home wifi gurgles. Apple's remote comes in handy at those times. You also will need a monitor. Price can dictate which way to go.

My .02 is to buy the cheapest Core i3 or i5, Windows 8.1 laptop you can find. Personally I hear no difference between a cheapo Samsung Book 4 that I picked up at Microcenter for $150 and my Microsoft Surface Pro 3 when either is plugged into my Ayre QB-9 DSD.

Mac mini. I have a dedicated Mac mini in my audio system with no attached disks, 16G of ram, and 1 of the best USB cables hooked to an external dac. My music is stored on a Seagate 5TB NAS central disk that I connect to it thru the wired network. I run my Mac mini headless, you don't need a monitor, keyboard or mouse, I use screen sharing from another mac or from my iPad using parallels. I actually rip my music using XLD from another mac onto the seagate NAS drive (itunes) so I can sync all of my apple devices to this iTunes repository of music. I use audirvana on the audio system Mac mini, I don't use the iTunes interface, I use audirvana's, sounds better but more crude in the interface right now. I use the parallels screen sharing program to interface with audirvana. I also have many TB of disks to perform different types of backups.
As far as ssd, I don't see the need for them. I actually have TB of SSD storage and the way my system is setup everything runs out of memory which is many times faster than SSD.

To me, the Mac still has the edge in industrial design and pride of ownership. That said, I use a PC laptop with an i5 processor, 8 gig of memory, and configure JRiver to play the music files from memory.

Really, for the task of delivering a digital stream to a USB DAC, about the only hardware thing that can interfere is disk drive thrash caused by not having enough memory, and the operating system having to swap things in and out of memory from disk. 8 gig should be more than enough when used as a music server.

However, it's important to optimize Windows to insure bit-perfect, hardware direct transmission to the DAC, and the chosen settings can be DAC dependent. These are normally set through the Windows control panel, but it isn't intuitive, so you either need instructions from someone like JRiver or Google the subject to find step-by-step instructions. The description of JRiver over at computeraudiophile.com has a good tutorial on the issues and options.