Can I Improve Sound--Macbook Pro as Music Server?

Optimize your Mac OS for music server

Reinstall the OS on a clean new partition preferably on an SSD

(this may not be applicable if you run the MBP as a multi purpose machine)
- disable spotlight
- disable IR
- disable Dashboard
- disable Spaces
- disable Energy Saving
- disable BT (and WiFi if you aren't using it)
- disable Time Machine

Use Audirvana Plus
- use A+'s System Optimizer
- enable Direct and Integer mode in A+ (should be supported by the USB-SPDIF device

If you are using a USB-SPDIF device like the Audiophileo, store the music on Network Server with a wired connection or use a Firewire/Thunderbolt external HDD (not USB).

New partition means a fresh installation, not an upgrade of an existing installation. I use "partition" as opposed to a disk because you may wish to create more than one partition (eg 1 for Bootcamp to run Windows and another to run Mac OS X for regular apps, ie not for music).

A network server (or network attached storage server aka NAS) is basically a dedicated computer that you can store far away from your music playback computer. It contains hard disks that are noisy so if you really like, you can keep them in a separate room away from your hifi equipment and use a wired network cable (Gbit recommended esp for hires music) to allow the music playback computer to gain access to the music files. The NAS also allows you to run arrays of drives for redundancy etc

A Thunderbolt port is a new interface available on newer Macs circa 2011 and up. So on most new Macs, you will have the option of USB or Thunderbolt (or USB, Thunderbolt or Firewire). Never use the same interface for the USB-SPDIF device (in this case yr Audiophileo) and the music storage, should you choose to use a local drive (vs a network storage system).

The MBP unibody is actually quite easy to open up. Apple even puts instructions online (to upgrade memory)

The new retina MBP on the other hand I'd not recommend opening.