I agree with just about everything above - particularly using a mixer unnecessarily in your signal chain.
One small point of disagreement - in a microphone signal chain, it's my opinion to be as judicious about the preamp as the microphone - if you have a decent microphone to begin with and this can mean a Shure SM57/58.
Judicious meaning get a pre-amp that can boost your mic input cleanly. Right now you are depending on a device, the Mackie, that has a bunch of other things on it's task list besides the microphone pre-amp.
You might be able to score a nice mic pre-amp for a couple hundred dollars that you can connect to your 2496 and be all set. As a fellow, mostly one-track-at-a-time recordist, this is all I needed for a very long time.
I recently upgraded to a Focusrite Scarlett 18i8 interface which is more convenient than what I had been using, and with very stable drivers, and with decent gain without noise.
I quickly listened to a few of your soundclick tracks. What exactly are you looking to improve? They sound decent. One thing I would do is lose the count-in on each of the songs. "Minor Mood" is the only one of the 4 or 5 that I listened to in which the harp sounds quite a bit more muddy than the rest of the BIAB supplied tracks. The harp is missing some high-end.
What type of microphone(s) are you using? And why does Minor Mood sound so much different than the others? It almost sounds like you have recording room issues going on - there's some notes which are considerably louder than others. For example, the note at the end of the phrase at 2:01-2:03 or so is probably 10 dB louder than other notes in the same song. What is your recording technique, room, etc.?
On some of the songs, it sounds like you are using a Green Bullet mic, like "Ivory Ike" which is cool, but it likely doesn't have high frequency response that you might be looking for. It has that great overdriven sound, but if you look at the mic specs:
http://cdn.shure.com/user_guide/upload/443/us_pro_520dx_ug.pdf you can see that the high frequency response has almost a 'brick wall' falloff right at 4 kHz. Sparkle happens above 4 kHz.
As to using a Scarlett with the Ketron - you might have to run the Ketron from the MIDI out of the Scarlett. It's possible your computer won't like two different USB audio devices in play at the same time. So that might be a change from what you are used to.