Designing "do all" products can be tough, those TAD amps may need their specific preamp to perform well. Adding the preamp may fix what is lacking overall, but impedance or whatever the case may be aside, more boxes will equate to more degradation of the signal. Adding the preamp may help the sound, but I worry you will lose some of the finesse the Discrete DAC has to offer. Sounds like a tough decision. I am a firm supporter of hearing before you buy... but doesn't sound like an option for you. Curious to hear how it resolves.