Music on NAS-Recommendations to play on HIFI

I have nearly a terabyte of music (in many formats) on a PC based NAS that I would like to listen to on my Audio System. Each system (PC, Audio) is physically close but electrically separate, and I want to keep it that way.

Here's what I've tried in the past:
1. Soundblaster audio output to preamp input. The sound was pretty good but there was the potential for ground loop hum to develop as both systems (PC and Audio) were on their own dedicated branch circuits. Absolute downside was that the PC's cooling fans were audible. I disconnected this arrangement because my audio preamp would go into a muted protection mode whenever my PC re-booted. The protection mode would occur regardless of what input was selected on the preamp. Not sure what happens when the PC reboots to elicit this protection mode, but for this reason I would like to keep the PC electrically isolated from the audio preamp.

2. Wireless Music Bridge. This method was pretty safe but the Linksys Wireless Music Bridge didn't have the greatest audio quality.
I could leave the noisy PC tower off and use a quiet laptop on my home network to access the NAS and play the files using the laptop's media player. A driver was installed on the laptop adding the wireless music bridge to the list of output devices (PC Speakers/SPDIF/Wireless Music Bridge). Everything was handled wirelessly over the network keeping my PC and Audio systems electrically separate but the overall sound depended on the quality of the Wireless Music Bridge.

So how do people do it? I have all this music stored on a NAS that I'd like to play through a decent DAC while keeping the two systems electrically separate. Any suggestions would be appreciated.
If I understand you correctly, you want to supply a 2nd system with files you have on a drive in another system without any physical, or electronic connections. There's probably several ways you can do this but I have a fairly simple solution that may work for you. 1 and 2 TB hard drives are very cheap. You really need to back up anyway so why not get a 2nd HD for use in your 2nd system. It can be your backup and your file source for the other system. Or maybe I didn't get what you are asking? Wouldn't be the first time I messed up a post.
this is how I would do it: connect a NAS to a wireless router via Cat6. All PCs should be able to see the NAS if they are on your network. set up a laptop that can see the NAS wirelessly, and use Jriver with Jplay plug-in installed to send music from the wirelessly connected NAS through a decent USB cable into a USB/SPDIF converter. Go from the converter to the DAC of your choice, then into the system. You can control the music selection on Jriver from an iPad using the Jremote app. Yes the laptop is tethered to the system, but you are mobile with the iPad.
Yes you can buy a DAC that has an integrated USB converter, but most of the affordable solutions for this IMHO are not as good as using a decent external converter. My converter/DAC combo cost me $600, not including the USB/SPDIF cable.
I have the files on my main computer and a NAS (Network Aware Server). The NAS is connected to the router and stands alone as a file server. In this manner, any computer on the local home network can access the NAS directly without having to share through my main computer. Each computer on the local network is assigned sharing privileges on the NAS, so one NAS can serve many computers on the local network and act as a backup.

Network aware servers have their own IP address just as any other device on the network, such as a network printer. In addition, NAS devices can be configured in a number of different RAID (Redundant-Array-(of) Inexpensive Drives) patterns, meaning the NAS can have 2 drives mirrored to protect the data if one drive happens to die. Sort of a self contained backup of the backup. Since they have their own IP address, it is also possible to grant sharing privileges to another computer outside of the local network, meaning I could grant access to a friend on the internet if I wanted to.

So rather than using the media player on my computer to access files on my computer's local drive(s), I can access the NAS instead. The NAS simply shows up in Windows "My Computer" as another drive. The big difference is that it shows up to any computer on my local network the same way, meaning it's always available even if every other computer is off. The NAS is gigabit fast and directly off the router, so it's faster than having one computer pull files from another computer over the network. It's really the best way to go. No need for each computer to have a backup drive, one big NAS can serve them all equally and offer superior protection.

I'm looking for a high quality Media Bridge between the NAS and an external DAC. To use the original Linksys Media Bridge, a driver was installed on the computer controlling the playback, only instead of choosing a speaker output or an spdif output, a new output device (Linksys Media Bridge) is installed and chosen. The playback then travels over the network to the media bridge which has L/R audio outputs.

The Linksys device works fine, I'm just looking for a more modern and higher quality product, something that has digital outputs to a high quality DAC.

How do people play digital files stored on a NAS without wires?
Look no further than Sonos. Easy setup, reliable, great interface for iPad, iPod, android, etc. I've been using it for 9 years.