Digital Keyboard into my RMB 1095

I am new to higher end audio products and was wondering what is the problem with plugging in my keyboard or ipod with headphone out into my amp's unbalaced RCA in? I do have a M-Audio Fast Track pro that has midi in/out and unbalanced RCA out that I think will work. It's a 24 bit DAC w/S/PDIF RCA in. Can I use it with my CD player that has that output? Thanks for the help.