I want software that plays sound files (wav or mp3) on background. Like, if I start the program and put "hello" into arguments, it plays file named hello on some specific folder. This needs to happen on background, I don't want to see anything.
Although I don't know of any such command-line-driven programs, remember that you can keep windows minimized. Winamp plays pretty much any audio file type. You can set it up for shuffle mode, track mode, track repeat, or repeat mode, pretty much your standard CD-player kind of thing. I don't know if Winamp supports playlists (I never use them). When you want to change songs, click on the minimized window in the task bar (or alt+tab) choose the song you want to play, and minimize it again. I have Winamp constantly running and I almost never see it, even though I haven't minimized it either.
Of course, there are other audio players around - Winamp is the only one I'm aware of. It's free and very flexible.
I use my voice to control my pc. I would like my pc to reply to those commands so that I know they are executed (some commands cause actions that I can't see unless I check and that defeats the purpose of using voice command to do it as I could just as well do it manually).
Because of that, I thought that some program was running all the time and my macros call it to play certain files.