The Zen CAN amp really can’t handle hi impedance cans, especially in the bass, like iFi claims. If you want to juice the bass of the 880 tho, I can confirm that the Zen Dac’s bass boost routed through a more powerful amp can get the 880 bumping pretty well. The G103s should do that for you.
I have more complete thoughts on Zec CAN here: 🔷 iFi ZEN CAN Headphone Amplifier - #3 by WaveTheory