Headphone out specifications 1(3.5mm port)
Output power 1 ≥125mW(16Ω / THD+N<1%) Output impedance <2Ω
Output power 2 ≥170mW(32Ω /THD+N<1%) THD+N <0.002%(1kHz/32Ω)
Output power 3 ≥19mW(300Ω / THD+N<1%) Separation >72dB
Frequency response 5Hz~80 kHz(-3dB) Peak output voltage 6.5Vp-p
SNR ≥118dB (A-weighted) Noise floor <5uV
Headphone out specifications 2(2.5mm port)
Output power 1 ≥125mW(16Ω / THD+N<1%) Output impedance <2Ω
Output power 2 ≥195mW(32Ω /THD+N<1%,balanced turbo off)
≥220mW(32Ω /THD+N<1%,balanced turbo on) THD+N <0.002%(1kHz/32Ω)
Output power 3 ≥24mW(300Ω / THD+N<1%,balanced turbo off)
≥77mW(300Ω / THD+N<1%,balanced turbo on) Separation >98dB
Frequency response 5Hz~80 kHz(-3dB) Peak output voltage 7.07Vp-p
SNR ≥113dB (A-weighted) Noise floor <10uV
If these numbers are correct then power output is more than ok!
Here are the specs for X7II.
http://m.fiio.net/en/products/71/parameters