12AU7 for DeHavilland 50A Amplifier

To all those "in the know"...  I have a pair of DeHavilland 50A mono blocks which use a 12au7 input tube.  The amps are a bit "soft" sounding in my system, lacking some of the leading edge transients which I had grown accustom to with my prior solid state amplifier.   I was curious as to whether replacing the current Amperex NOS 12au7's with the Gold Lion reissue 12au7's (the amps were designed around, and use, the Gold Lion KT88 power tubes) would give a bit  more of a well defined transient type of presentation, or would I be giving up too much sonic beauty that the Amperex tubes provide?  FWIW, I tried (with Kara's OK) substituting the KT88's with KT150's, and wound up returning to the KT88's as the KT150's proved to be a little too lean.
Thanks for all your input on this...