Hey 20,
The 24/192 files *are* in .wav format. RuneAudio will play .flac, .aac and .alac, I believe. I don't have anything in those other formats, though it sounds like they are all working well.
I store my music on a couple larger-format USB thumb drives. Other options are NAS drives, and external USB drives, so long as they have their own power source. The Raspberry Pi boards only offer 2A of power throughput, so things that spin up a drive or are large current draws don't work well. For instance, I have a spin-up external USB hard drive that requires USB power, so I could only use that by attaching it to my NAS ready router. Not real difficult.
The player is the RuneAudio operating system on the Raspberry PI (B+ model in my case.) The RuneOS paired with the onboard Rpi computer directs the file stream through the I2S pins into my onboard dac. You might choose a different DAC board, or a digital tolsink output board, or just use the raspberry pi USB ports to out put to a standalone DAC. In the above photo you can sort of see the secondary board stacked on top? That's the HiFiBerry DAC board. It comes with standard RCA jacks, which I desoldered so I could wire the board to external jacks. I like the short circuit path as much as anything. The first iteration of this was literally the stacked boards sitting behind my AV cabinet. Worked like a charm, though not as pretty.
In this photo you can see the backside of my build. Power in, a fuse holder, RCA analog outputs, USB ports with one flash drive for media storage, and an ethernet port. In my setup I've hardwired the RPi via CAT-5 to my router, and I access/manage the whole thing wirelessly with a tablet through my router. You can evidently use a wireless dongle to accomplish the same thing if you don't want to run CAT-5, but there are still a few bugs being worked out in that department.
My technical writing skills are... still improving. A feature list can be found here... http://www.runeaudio.com/features/ Hopefully that answers some of your questions? Hit me up if you have more, I am happy to help where I can.
Cheers!
-Fishstix