The only thing I found was to assign a global value to constantly record the position of direct show, and in the next frame load the position of direct show to the global value.
But there will still be a tiny gap in between frames and the music. The best thing to do is convert your files to OGG Vorbis and play them thru the sample menu in the event editor. That's what I'm doing now with Castlevania and the results are flawless, especially if you dig into something like Sound Forge and edit the song to where it can loop without noticing it restarted.