I don't quite understand the problems reported here for the Sweet MIDI Player.
I started using the demo (downloaded from Roni Music) as soon as it was available for my Intel iMac G5, and apart from the muting thing (which has just been fixed), it's the best player I've ever found for my purpose.
As a music teacher I use MIDI a lot to create music "minus one" play alongs for my students. In fact a number of my students have downloaded the demo for Windows also without problems.
Just make sure you download the latest version from Roni Music.