Correct - in addition to the traction system, all train heating on 319s (and 769s) is electric directly off the 750v busline, they don't use waste engine heat like the majority of DMUs. The air compressor is also very power hungry, again running off the 750v busline and the lower voltage electrical systems (425v AC, 110v DC, 24v AC) are supplied by a motor alternator which runs off, guess what, the 750v busline.
The 110v DC control voltage alone on 769s will have been converted from ~900-1000v AC produced by the alternators on the new engines, rectified to 750v DC, through the smoothing choke, run the MA set to produce the 415v AC which is then stepped down and rectified again to 110v DC.
769s will not be electrically efficient machines.