I appreciate your short write-up & thoughts on this modded HiFace USB transport "yoke". It was great to hear it through Ivor's high-end playback system, I had only listened via cheap Sony headphones or my Tripath class D amp.
Just to let people get an idea of the size & how it all fits together here's a pic of the unit with battery attached

We didn't do any listening to the plugin ESS DAC that I brought as we didn't have the connectors. Here's the technical bit, this DAC is being fed I2S from the HiFace USB transport which is superior to SPDIF as a means of digital audio connection.
Here's the DAC (in raw form) plugged into the HiFace

One interesting discovery - I borrowed Sennheiser HD650 headphones & Millet Hybrid Max headphone amplifier from Fran to have a listen. As I said I'd mainly listened to cheap Sony MDR XD200 headphones up to now. This ESS DAC when connected directly to the HD650s drove them beautifully which surprised me so I plugged in the Millet headphone amp and ran the DAC output through it into the HD650s - no difference in sound that I could discern!
This combination is an amazingly good portable USB transport/DAC/Headphone driver!
As Fran says more testing will be entered into with various DACs & headphones - More to come :)