Hi Dee,
Don't know if this will help, but since you have such a small setup (like me) and you're not using a multitracker for recording, perhaps you could do without the midiman midi interface. I have a setup similar to yours, perhaps less advanced:
p400MHz 128MB
Behringer 1604A mixer
Korg X5D
Akai S900
Logic Audio Platinum and SB Live!
and my system runs in perfect audio sync without the aid of a midi interface?

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Regards