EJ, not sure what your problem is, as there's no explanation of your software, setup and settings...I have the exact same soundcard and latency/not getting cracks depends on many factors.
May be even worth feeding it into a midi monitor.
(I don't have a sidecar, but may get round to doing this with the rang itself)
That's a bit of a cryptic answer, could just mean that the midi commands
aren't those commonly found in commercial controllers.
It could be weird MIDI (RPN/NRPN or sysex). I'll try feeding it to a midi monitor tonight. It would be nice to have an alternative controller and some message sequencing options for the boomerang.