what power tubes are you using in the Shanglings? I don't own your amps, but have been using EH 6CA7 output tubes with great success. They still have the fantastic midrange of an EL34, but bring some of the KT dynamics and improved bass. On top of that, they are very inexpensive.
Regarding your question to replace preamp: I find an octal tube based preamp provides superior frequency response and dynamics that a miniature nine-pin cannot touch. So you might want to consider keeping your existing preamp.
Regarding your question to replace preamp: I find an octal tube based preamp provides superior frequency response and dynamics that a miniature nine-pin cannot touch. So you might want to consider keeping your existing preamp.