Let's look at your usual MP3 file. I see an average 5 MB.
This means your 500GB drive could hold 100,000 songs. At Apple prices that's some 100,000 DOLLARS of songs. Even at 50 cents a song that's 50 grand of media so there is little reason to produce such a device.
Even so, if you do look at newegg.com you will find some media boxes that exist as well as other solutions. But just the sheer cost of the media makes such a system not viable for the retail market.
So, here's the thing: I want to listen to MP3s on my home stereo and NOT have a computer connected. In other words, I don't want to stream from a computer to my stereo. I could go into "why" but there are too many reasons to list. Mainly, inconvenience.
I also don't want an iPod type of device. I have no interest in listening to music "on the go" and the storage capacity of those devices is too small; and the audio connectors and quality is relatively poor.
Here's what I envision: a device the size of a DVD player that fits as a component on my stereo shelf. It has a display on the front similar to an iPod or such a device. On the back, it has a USB port where I can plug in a portable hard drive, such as a 500GB hard drive full of MP3s. It also has good quality connectors to connect to my amplifier.
Does such a device exist?