This is exactly what I think. I understand each tube has a different characteristic. So, I bought the Modwright LS100 which use the 6SN7. Eventually, I choose the slightly more open sound of CSLS over the excellent tone of the Modwright. I know I cannot judge the sound of a tube by just one amp, but I feel 6SN7 tube is lacking the fineness and transparency in 101D. So, if I am going to try another preamp, I would like to try one with a different tube.
Since I am quite satisfied with the current setup, I am not going to make decision light heartedly. Thanks for all the feedback.