I have read that a 5 car electric IET is rated at 2712Kw or 3641 Hp. The 9 car units are said to be 4520KW or 6070HP. So around 14hp/ton.
A 5 car unit has 3 diesel engines rated at a maximum of 700 KW or 940hp each. That is 2100Kw or 2820Hp,
The 9 car units have 5 diesel engines - so a toal of 3500Kw or 4700 Hp.
Of course the diesel engines have to supply power to the trains computer and control systems, air conditioning, power doors, lighting and auxiliary systems. So the power to rail is going to be less than this. An HST only delivers 78% of its installed diesel engine output to the rail, 3540 hp rather than the 4500Hp quoted. So it is fair to say that an IET would probably at maximum offer a similar percentage to the rail. Based on a 78% diesel output to the rails, that would be 2200 HP for a 5-car and 3666 HP for a 9-car IEt. Despite the fact that newer trains have more efficient traction packages, and LED lighting, i would imagine that chemical retention toilets, passenger information systems, and the vast computer control systems balance things out - possibly even consuming more than the basic auxiliary systems aboard HST power cars and Mk3 coaches. I'm sure the real information is way too commercially sensitive to be revealed here.
I think you are rather over-egging the situation...
A simple sanity check will give an idea of the orders of magnitude the various systems use.
Locomotives have an ETH (Electric Train Heating) Index to allow easy calculation of the length of train the locomotive can heat or cool. 1 ETH unit equates to 5kW. A Class 92 has an ETH Index of 108 which is compatible with the 16 coach long Anglo-Scottish sleepers. This translates to a total ETH power supply of some 540kW which, divided by 16, gives a consumption of 33.75kW per coach.
The power required for heating and cooling an IET coach will be about the same, the extra 3 metres in the coach's lengths will not make much difference and modern air conditioning plant is probably slightly more efficient than the Mark 3 coach's nearly 50 year old design. In the IET's favour the gangways seal better than the Pullman-style gangways used on earlier stock so the power draw may be less.
However, if we assume an ETH load for the IET as being 35kW per coach this gives a total of 175kW for a 5 coach train. This is just over 8% of the total diesel power available with the engines at their 700kW rating. It might be a bit more or a bit less, but whatever the actual value is it won't be greatly different.
The major losses between the engine's power measured at the flywheel and the road wheels are the losses in the main alternator, losses in the power conditioning circuits and the drive motors and gearboxes. Also to be subtracted from the nominal output power, in addition to the train heating supply, is the power drawn by the radiator fans, air compressors and battery chargers. Not all of these thing run at the same time, but 80% of the nominal diesel engine output power available at the wheel rims is par for the course.
The other consumers pale by comparison. Power drawn by the power doors is irrelevant - normally the doors are only operated when the train is stationary... A powerful desktop computer draws 450 to 500 watts, say that there is one in each coach and there is also a WiFi router in each coach which draws the same, thats 1 kW per coach or 5 kW for a 5 coach train - about 0.25% of the nominal engine power. Power drawn by the electronic displays is negligible - if it wasn't your laptop would run flat in an hour or so. The toilets run for a few seconds every five minutes - and that is if the passengers have been drinking...