The RealDrums are audio files. They will use your sound card for output. The Ensoniq can be interfaced with BIAB as long as the synth and your computer have the ports (midi or usb) to do it. If you use your Ensoniq and want to use RealDrums, you would have to balance the audio output to match the midi output of your Ensoniq. If you want to use the Ensoniq drums, you can 'turn off' the RealDrums and use the Midi drums. But after you hear the RealDrums, you probably won't want to do that. They are very good.

Recording using an external synth is only a matter of mixing the synth and the RealDrums into your recording device.

Rachael