To run two pair of monitors from one SET amp

I have a Assemblage 300B Platinum amp which is running a pair of full range driver speakers. Nevertheless, I have fallen for a pair of AKG K1000 headphones, which happen to be really affordable and yet extremely inefficient. These headphones need their own amp, with a minimum of 7 watts per channel (Efficiency around 74db.) So, instead of buying a separate amp, I thought about getting a speaker switcher such as those that NILES makes. When I read the website information, it said that it would work with amps that can drive at 4 ohms. I think this switcher halves the impedance of the amp in other to drive two sets of speakers. These are the questions I have....#1-Will the NILES affect the quality of sound that goes into the monitors (both Speaker and headphones)? #2-Is an SET amp such as Assemblage 300B with three heavy transformers break a sweat working driving 4 ohms? #3 Which is better, get its own amp to drive the AKGs...because my preamp has two outputs? #4-If I go the way of 3, then, if I do not turn on the SET amp, it will not in any way affect anything down the chain, right?
PAUL