Yes, I built a few headphone amplifiers using a similar setup: switching power supply - EMI filter - rail splitter - amplifier. No noise, just wonderful sound.
At work the SD cards lasted for about 1,5 year and then gave up.
I now disabled Ext4 journaling and am considering using the F2FS filesystem which is designed for flash storage.
Smallwall (http://smallwall.org), the successor of M0n0wall: not many 'moving parts', rock-solid. Saves a lot of time comparing to building it yourself (software-wise).