Im with those above here on the JD. I run my stock 100 with RCA 5751 3Xmica Black plates...the best so far. The Raytheon 5751's with windmill type getters are indeed very good as are GE's...but the RCA's took it up another notch. Very similar to the Ray's..but better bass and even more palpable mids. These tubes provide an incredible increase in focus and detail over the 12AX tubes, and are much smoother on top than the stock 12AX7's.. Refines the sound if you will.
Having heard the Level 2 mod for myself, I found that it did provide a bigger and more dynamic presentation, but seemed to have lost some of the mid magic of the stock player. Overall the stock player with tube upgrade is the best bang for the buck, and keeps the warm sounding mids intact better than the upgrade to my ears. Use an excellent power cord and the use of some good point isolation cones under the player in a tri-point set up, and you have a great sounding player. I think the sound betters my Wadia 23/Electrocompanient ECD-1 24/192 player/ DAC combo.