Sure, this is probably more information than you want.
I'll keep to the 5 car sets on both, since it makes it a bit shorter, but the 7/9 car 80Xs behave the same way, but with extra motor/trailer vehicles.
Class 80X
Formed as: Driving Pantograph Trailer + Motor + Motor + Motor + Driving Pantograph Trailer
There's a high-voltage AC* bus fed from the pantographs that spans the length of the entire unit (you can see the "pigtails" at the top between vehicles) and a 400V APS bus for hotel power. Each motor vehicle can draw power of the high-voltage AC bus or from the generator unit (if installed).
Motor vehicles each have 4 bogie-mounted 226kW self-ventilated motors
[details]. The motor vehicles are responsible for driving their motors and providing an APS bus supply. They also have emergency batteries.
The APS bus can cross-feed between vehicles to provide APS power to trailer vehicles and vehicles with a failed generator unit.
Traction power is not cross-fed. You'll notice that motor vehicles with a failed generator unit won't be putting down any power on the rails on diesel. With only diesel engines, there'd be no advantage in cross-feeding generator unit power since one motor car can put down more power than its engine pack can provide.
As far as I understand, the class 395s are the same but with slightly different motors
[details] and the generator unit supply instead being used for third rail. The class 395s, being a similar proven design, helped Hitachi win the IEP contract. It's worth bearing in mind that the bimode IEPs were originally intended for only 100mph on diesel...
Image Description - Diagram of the Traction/Auxilliary Power System. Credit: Hitachi.
Class 810
Formed as: Driving Pantograph Trailer + Motor + Trailer + Motor + Driving Pantograph Trailer
The 810s aren't dissimilar, but only have two motor cars. To compensate for this, they have 250kW motors instead. To match 22X timings, each motor car has two diesel engines as its generator supply, one located on the motor vehicle and the other on the adjacent driving vehicle.
There is no traction power sharing between two motor vehicles. You can treat them the same as the 80X motor vehicles; they just have one engine on an adjacent trailer due to limited space.
To bring it back to XC... the 80Xs were originally designed as 140mph electric / 100mph diesel, and as such lack the performance XC needs. The 810s would be better suited but have a lower capacity (24m vs 26m) compared to 80Xs, and a 7-car variant would require a little bit of design work since you'd need a non-driving trailer with an engine.