I just looked up your tascam, it has 4 preamps, unless you are needing to record all the parts at once, you don't need to buy a preamp.
If you are getting noise from plugging the keyboard directly in, you need a di box that will plug into the xlr inputs on the neo.
You have two problems with both mixes:
1. as was mentioned before, all the parts are in the same octave, so they are using the same batch of frequencies, (mostly lower mid, in this case)
2. You aren't doing anything with the upper midrange on any of the instruments.
For the bass, add a couple db of 800hz and a db or two of high shelf at 2-3k. This will balance against the low end and (maybe) allow you to drop the volume while still hearing it clearly.
I'm having a hard time identifying the instruments that are playing, but there is something with an envelope follower, or wah...brighten that up (3-5k), or suck out some 200hz..or both
Add a little bit of 1k and high shelf at 8k to the Rhodes
Start doing stuff like that, if you can't go back and play some of the parts in a different octave.
The trick is to give every instrument it's own space to occupy. You can do that with the arrangement, by making sure that each instrument has a part that doesn't clash or step on another part. This can be done with instrument choice and octave choice. More than one instrument can occupy the same octave, if they sound different enough from each other. (guitar and trumpet, for example)
Also, you can use EQ to carve out space for different instruments. For example, the note definition of bass is around 800hz, so you let the bass occupy that and give the Rhodes 1khz. So you carve a little 800hz out of the rhodes and add it to the bass. Do that with all instruments that are conflicting with each other. The sound of the instrument by itself doesn't matter, how it fits in the mix does.