If you can hear it you should at the very least be able solo it, send it out the sound card output and record it back in to another track in RB.
You can probably do the above 'inside the machine' but that depends on your sound card or audio interface and your knowledge of how to use it.

You may also be able to 'Render' it to it's own wav file and import that back into RB as another thing to try.
In this case, again, Solo the track and then Render Audio and DXi tracks to wave file.. or possibly even just Save Track to file may work. (If RB asks about silence at the beginning answer Yes; it helps line things up when you import to the beginning of the song)

Just a couple ideas. I generally use hardware more than softsynths, but the above options *should* yield some joy.
Because I use hardware I am commonly sending the recorded signal (usually MIDI) out and recording the resulting audio back in, which is just a variation of my first suggestion above. I have also sent audio out, ran it thru some device and recorded it back in, so it should work.



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