Having lived with the DEXA Discrete op-amps for about 3 weeks now, they really do seem to be the one's to beat. I highly recommend for the tube output the Philips E80CC pinched waist D getter version as a substitute for the 12au7. Although this tubes is twice the length and you won't be able to put the tube shield in place anymore , and being that this isn't a direct substitute for the 12AU7 as it draws twice as much heater current, Alex Yeung the designer says it is ok to use. This tube with the Dexa's is fantastic!