"I just got my own stock Orchid with WE 369 tube. The mid range from it is the best I have ever heard in years. Very detailed, smooth and musical.
However, there are some areas that I wish it can improve: the dynamics, high and bass. Do you think that Orchid should be more dynamic, the bass should be tighter, and high should be more airy? I believe these areas can somehow improve by upgrades..."
quanghuy147, try the Tesla 2C51/6CC42 tube in the Orchid instead (if) your main preamplifier and amplifier are already smooth sounding. The WE396 does have nice mids, partly at the expense of rolled highs and less dynamic, exactly +1 what @grannyring said about it.
The Tesla 2C51 in the MHDT Orchid is right between the stock GE 5670 5-Star Triple Mica and the softer WE396A. If you want to brighten up and get back some detail on the top/bottom end, actually the stock GE 5670 5-star triple mica is not bad, but I prefer the Tesla with my particular tube preamp and mono block tube amps. It’s like spices on a meal. A little here and there, not too much.