I have a Mackie Thump15 15-Inch powered loudspeaker that I want to be able to play music from my iTunes library on. The speaker has active amplification and has a mic and line input. I read that I can simply plug my iPhone or Mac headphone jack into the line input with the volume turned way down, but because of the amplification of the headphone jack, the quality would be less than that of using a less amplified line input. I have looked into preamps that allow MP3 or usb input, but I know very little about this and I'm not sure I can make an educated decision on my own. I have endless computing resources I could use to connect to the speaker, but the problem is I'm not sure how, or what is the best way. I am not a DJ, so I would have no use for mixers and DJ software. I would prefer a high quality solution, but I also don't want to spend too much money to do it.
Edits: As it stands I currently have one speaker. However, in the future I may eventually get another, but that is a long ways off.