input tube rolling on manley neo classic 250's

the amps come with EI 12au7's,they sound good except i would like a little more on top,i tried the siemans nos and they made the midrange sound very thin and the top end was so so,i have tried mullard nos and the top was to die for,but the base was soft and the midrange was very layed back,not what i am looking for,I do love these amps otherwise,any thoughts

Michael.