If the use case you described is the only use for the device, Octatrack sounds a bit overkill. If you have an iOS device lying around, I suggest you check the software called AUM: http://kymatica.com/Software/AUM. It can stream several audiofiles simultaneously quite reliably. Of course, then you would need an audio interface as well, but perhaps you could test it with two mono tracks from the headphone output.
I had to make a similar choice recently, and instead of (re)buying an Octatrack, I just decided to use an iPad and AUM. No gigs yet, but works fine in a rehearsal setting.
But Octatrack is great. Really miss mine. =(