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i am not familiar with SPDIF
but why don't you sync Logic and SP with MIDI and then use RCA-dual phono cord to record the audio?

Have you tried a different set of inputs on your soundcard?

I'm not familiar with that box, but SPDIF (digital) is not really RCA (analog)- although the connectors look the same. You'd need something with a digital output (SP-606) to interface with that input.
The box must have some analog inputs eh? 1/4" ?
Just get some RCA to 1/4" adapters (Radio Shack) and go analog.

I think

hXc is right on the money here.

Watch out what you're doing, because basically it can damage your device if you're connecting that way!!

I made the same mistake with my MV and I almost broke things.

SP-303 has no SPDF output. you need RCA to 1/4" cables to record.

I used to do the same thing. SPDIF is a digital in/out. I don't know of any people who use this, though I heard it yields good results. But in order to use them, both pieces must have digital ins/outs. You need a 2 rca - 2 quarter In. cable. hope that helps.