I have the JD-100. If your looking for smooth-it's the one-if your looking for detail, it aint the one.
BUT, with a little work - it's very good , IMO.
I'm using tubes as well and when I first got the player, ( a year ago), I was quite disapointed. Too opauge sounding for me. It replaced a Nohr CD-1 or more accuratly the oem version the QDS-15. The QDS was far more revealing and real sounding.
I soon wished that I had purchased the JD-100 with the available mods.
So, naturally, I modded it. If you check out the Underwood Wally web site, you'll find the available mods. I believe they're available in levels 1, 2 and 3. I've now got mine fully modded accept for the resistor swap. I have done all the changes myself and the cost was about $150.
The single most important mod is to get rid of the horrible polyester coupling caps and replace them with something decent-I used Sonicaps-HUGE improvement. Detail and clarity now came through as it should. If your not willing to do the mod or have it done through a dealer, (warranty intact through dealer), I wouldn't recommend the player. If you do the mod,(s), also consider a nice pair of N.O.S tubes such as Brimar 12ax7's. These are the best I've found so far, even surpassing the Sylvania black plates.