It's often useful to understand "how" before trying to determine "what"...
Given an input of a bunch of FLAC files in digital format on a hard drive and given that the requirement is to provide an analogue line-level signal to an input on a pre-amp, just "how" any solution needs to operate to achieve integrating the inputs to the desired output.
Firstly, the hard drive would have been formatted on some form of computer running an operating system. The operating system used will tend to determine the file system used to format the hard disk. The file system defines how files are written to / read from a hard drive as well as what metadata fields are written per file. If the hard drive was formatted under Windows, there are two common file system options: FAT32 and NTFS. FAT32 is useable on Apple Macs but NTFS is not. So, it is key to understand the file system used when the hard drive was formatted.
NB: If the hard drive was formatted using NTFS and you want to use an Apple Mac to read the hard drive, you will have to backup the hard drive, reformat the drive to FAT32 file system and then restore the files to the now-reformatted drive.
Next, any device that needs to retrieve FLAC files from the hard drive will need either a SATA/eSATA connector or a USB connector plus the controller hardware required to drive the port. Then, the said device will need to be able to communicate the files available on the hard drive to prospective listener - usually via some visual display device (eg a TV or a smaller, less obtrusive computer monitor). Next, this device needs to provide the user with a mechanism to navigate through the list of available files and to select one (or more) files to be played (or queued for play). Once the user instructs the device to commence playing, the device needs to retrieve the digital FLAC file, feed it through some form of Digital-to-Analogue Converter before channelling the signal to a line-level output.
Yes, it is possible to "knock together" a number of different solutions, each offering varying levels of cost and WAF. An RPi-based solution would be reasonably inexpensive but would still need a screen plus some hardware/software to permit a smartphone to function as a remote control.
At the other end of the cost spectrum one can buy audio-focussed integrated media players which come with everything packaged in a neat 19" standard audio component (eg Cambridge Audio's CX-N) - incorporating all of the necessary circuitry to manage the external hard drive, manage the display formats required to communicate options to the user, incorporate an in-built display on the fascia, provide remote control devices to enable navigation, incorporate audiophile-grade digital-to-analogue conversion (with up-sampling) and with audio-grade circuitry/disciplines in build. But these are not usually that cheap...
Somewhere in the middle, lies a third option which takes care of disk drive interfacing, user interfacing (display-driver and remote input) but lacks the facilities of a physical screen and lacks any digital-to-analogue conversion. This option relies on the use of a reasonably inexpensive video-focussed media player (such as Western Digital's TV) plus an el-cheapo and small PC monitor and also relies on the prospective already having a digital-to-analogue converter with a spare digital input (typically TosLink). The media player incorporates all of the functions to manage the hard drive, and manage the communication back and forth with the user, lacking only the display and audio signal conversion.
I tried out this third option using a Seagate GoFlex TV media player together with a 23" monitor and feeding TosLink optical digital output into my Bryston BDA-1 DAC. It worked - and quite acceptably too - but lacked adequate WAF to be a viable long-term solution for the main audio rig in the lounge.
Currently a similar set-up is still in use in the study where an Asus media player feeds both a TV and a small Denon amp and the TV provides the GUI, the Asus provides the remote and the Denon handles the audio to a pair of small Tannoy speakers.
Since that time, a neighbour bought a Cambridge Audio CX-N to fulfil the function you describe and, having played with it a few times, I am quite impressed (and a little bit envious).
If you're someone who does not stay satisfied with half-baked solutions, I'd strongly recommend a visit to your nearest Cambridge Audio dealer...
Hope that helps...
Dave
