We're all trying to find the best bang for the buck, so something may sound nice, but not really be competitive within it's price class. "Seriously nice sounding", is unfortunately not a comparative statement.
When I owned the 640P I found it bettered by every other phono stage that I had at the time. That would include the Creek, Musical Fidelity, Musical Surroundings, Graham Slee, Radio Shack and Shure. YMMV, but I would cut and run. Putting a band aid on it won't get you there.
For three large used you could have a Phonomena, Gram Amp 2SE, or Hagermann, which are all in another class. Just my 2 cents.