Headphone amp connection - best sound quality?

I'm hoping someone could give me an idea on the best way to integrate a headphone amplifier (not yet purchased) into my main listening system. I would mainly use it to listen to just one source (Wadia 170i/Audio Note DAC) and I see 3 options:

1. Connect the tape out RCAs on the Musical Fidelity A5 integrated to the RCA inputs of the Headphone amp; or

2. Use an RCA splitter on the anologue outputs of my source (Audio Note DAC One Sig.), to enable direct connection of the source to both the headphone amp and the integrated amp; or

3. Install an output selector device (assuming these exist) after the source and then run interconnects to the headphone amp and integrated from this device. This would enable me to select to which amplifier I want the signal sent.

I'd like to know which option would provide the cleanest signal. In option 1, I assume that the fact that the source has to go via the integrated amp line in/line out circuitry, this would not be as clean as a direct from source connection. In option 2, I assume that if both amps are switched on, the DAC would feed a signal to both - would this still be the same case if one of the amps was switched off? What would this option mean for the output voltage level of the signal. If option 3 is viable, can anyone recommend one of these devices.

Any help greatly appreciated.