Sounds like you had some fun. You might try a version with the upright bass being a bit dryer..emulate a small room with a close-mic technique. I was gonna suggest substracting a coupla dB of low end and hi end off the bass instrument (a safer way to raise the mid frequencies), but I would hold off on that until after you've heard it with a changed room environment.
I agree with Rudy on the dryer sound to the bass plus maybe move the piano back a bit it kind of overshadows the bass a bit.
Whatever, on the musical side it is great! Nice feel. So you say you got an upright bass? Cool sounds nice!