Music sounds flat stored on the hard drive

I have a problem. I found out when I connected my CD player to my Node 2i. What a beautiful sound I thought and what a difference with the music on my hard drive. This hard drive is connected to my router. Then i put a number of files on a USB stick. This stick connected to my Node 2i and then it sounded much better. But I want to control my music via the router since I occasionally put new music on it. So I don't know what I can do about this either. So why sounds my music stored on the hard drive flat? I have a WD drive with no separate power.