Well after 6 months of having used my iESL with only the Pro iCAN previously, I can now finally say I enjoy it! As I and others have stated, using the HDMI connection to power it isn't ideal. Difficult to get at a good volume without distortion and/or tripping the iCAN from overheating.
I upgraded to the Chord Hugo TT2 largely in hopes of it improving the iESL and the 2 headphones I use with it. My special cable arrived today to be able to power the iESL directly from the balanced outs in amp & high gain mode from the TT2. I was about to give up on electrostatics altogether and had wondered if my iESL was defective. Nope, finally amazing! Can be blasted without distortion and the sound is so much more full and pleasing. The Stax SR-007s have finally become TOTL sounding and even the Koss ESP/95X sounds better than I imagined it could. Both are now completely different headphones!
Alternatively I connected the TT2 to the iCAN balanced and powered the iESL with the HDMI cable. While that was an improvement over having the same DAC connected via RCA in DAC mode, it's just so much better going directly to the iESL via balanced & amp mode. You'll need
one of these cables though.
So if you're not thrilled with the iCAN/iESL HDMI setup, don't give up and try driving the iESL via XLR with a more powerful amp. The iCAN pairing with the TT2 with non-electrostatics is also pretty amazing.