Bobby9999... I use a KETRON SD2 and a Mixer too.

My Mixer has neither a USB nor a Firewire Connection to the PC, but I use a TASCAM audio interface... Since your Mixer has a Firewire buit-in Audio Interface, obviously you wouldn't need the TASCAM-like device.

However, you need a Midi interface. I use an inexpensive USB/Midi cable ($39), or Roland has one too UM-2G ($49)... All you have to do is first connect the SD2 to the PC using this midi interface... In BIAB, you won't see SD2 in the Midi Driver/Setup under Opts. You'll only see the name of the Midi Interface (i.e. UM-2G) or whatever you end up using.

So the midi signal will be sent form the BIAB to the ketron, first. Once the KETRON processes the Midi instructions, it will generate the audio/WAV signal, which is then sent to your Mixer via RCA Cables (I use a Y adapter Cable, RCA to Mono 1/4" jack, and plug it in one of the Line-in Channels.)

The other audio sounds coming from the BIAB (if you have RealDrums, Realtracks, etc mixed with Midi) will come to the Mixer via your Firewire connection.

If you just want to hear the music, and if you have your speakers connected to your Mixer, you'll hear the combined mixed sound come out of the speakers...

If you want to record, it's a bit different matter... you don't want to create feedback by looping the sounds already recorded (or already being generated on your PC, such as Realtracks) to be sent back and be re-recorded on your PC. You only want to send to your PC, only new Audio... i.e. audio created by the ketron, maybe your MIC, or guitar you are playing... etc.)

To do that, I hope your Mixer has a Sub Channel...

Only send the sounds you want to record to the Sub Channel, and then "send" the sub channel to the PC via the Firewire... [You may want to read in the manual how to do this... I haven't used a combo Mixer/Audio device... but it should be a matter of pressing the right buttons...] In my case, I take the output from the back of the mixer where it says Alt3-4 and plug it into my TASCAM Line In... and that's the only thing that goes back to the PC...

On BIAB you only have one track to record. In RealBand, you have 48! Each time you record an instrument, you may have to do it in real-time.... one track at a time....

Good Luck.

2008 Gibson ES-339 Custom & 2010 Les Paul Traditional. Fender SCXD Amp
BIAB/RB 2015 UltraPAK + Ketron SD2
Windows 7/64 Intel i5 3550 PC, Tascam USB144MKII
Behringer X1204 Mixer
Bose Companion 3 and/or L1 II w/T1 + SM58 MIC