Yes, you can do this (hard drive connected to your system). Apple/mac makes a product with this basic approach. There is a large variety of hard drives available, blue tooth, wifi, wired, et al. Several years ago when I was buying an external hard drive I considered this. I don't recall the specific hard drive manufacturer I looked at, but it allowed for this general approach (no iphone app at the time).
The thing I didn't like about it was the fact that many external hard drives are loud and that noise from one would drive me crazy in my listening room.
The thing I didn't like about it was the fact that many external hard drives are loud and that noise from one would drive me crazy in my listening room.