I highly suspect the impedance level is not that low. I tested it with shure 846 (9ohm) and ZX1 stock with Dac port (1 ohm), Imod & Pico slim (less than 1 ohm), M8 (1 ohm switch), zana duex se (3ohm) and this is my findings;
The ZX1 has slightly more bass overall and less treble as compared to these other amp/dac mention above which lead me to suspect the impedance level is highly unlikely to be at 1ohm. When I compared it with M8 at 10 ohm switch, the bass of M8 bass is slightly more than zx1 and treble is more recessed than zx1, this findings lead me to believe that the hope of getting 1ohm level is almost out of the window. But then again, the added bass slam is much needed here, so what I did, I added +2db on 16K and +1db on 6K and the treble now sound a lot closer to a 1 ohm mode treble quantity and now I still have the added bass that comes with higher impedance (I call this cheating mode).
I am only suspecting until someone measure it to confirm my findings. I think its around 8-15 ohm imp level but I am speculating.