C6 suspension : Hydractive 4(?)

Below are a few photos of the C6 that more or less clearly show the rear supension of the Citroën C6.

As can been seen from the pictures there are two height sensor pro axis, that is one for each wheel. In the middle between the wheels there is "hydraulic bloc" with two extra spheres.

Many thanks to Fructidor for sending me these photos !!
 
The construction of the rear axis is more easy to understand when looking at the rear axis of the Peugeot 407, which is almost identical. On the C6 the spring and damper are replaced by the suspensions cylinder and suspension sphere. Unfortunately the drawing below shows the 407 axis from the front, where the photos of the C6 are taken von behind.
Since the sphere can not be used as the "end" of the suspension cylinder, the sphere is mounted in angle to the suspension cylinder, just like the front spheres (on a XM for example).

The complete Peugeot 407 rear axis (picture from Peugeot) Detail of 407 rear axis (picture from Peugeot)
The right height sensor is green, the left is blue!

Since the C6 has these separate height sensors per wheel it might be equipped with an Activa function to actively correct body roll. Instead of using a separate hydraulic ram in the anti-roll bar, as on the Xantia Activa the C6 could use the individual suspension cylinders to correct the height at each wheel seperately.
The function of the two extra spheres mounted on the central "hydraulic bloc"  leaves me puzzled. Obviously (?) the central block is directly connected to the two suspension cylinders by means of the the two rather thick tubes. Also puzzling is the pressure sensor (?) mounted on the tube going to the right suspension cylinder.

There are several possibilities for what the two extra spheres are being used for:
  1. Two spheres pro side:
    Each suspension cylinder might have two spheres, one mounted on top of the suspension cylinder and a second one mounted on this bloc. In the case the second sphere can most probably be connected / disconnected to/from the other. This would mean that the two spring rate can be changed pro wheel and not just pro axis (as on a XM, Xantia or C5).
    I'm not sure if this would be a usefull feature.
  2. One sphere pro side + two common center spheres:
    The two center spheres could also be connected to (and disconnected from) both suspension cylinders at the same time. By connecting zero, one or two center sphere to both outer spheres at the same time the spring rate of one axis could be changed between at least three different values (instead of just two values on a XM, Xantia or C5)
  3. Spheres as pressure reservoirs for Activa functionality:
    Active body control during driving has to happen very quickly, i.e. within milliseconds. This would require quite a lot of hydraulic power within a very short time. I can imagine that the two extra spheres act as pressure reservoirs that can supply extra hydraulic fluid (to the suspension cylinders) under high pressures almost instantaneously, thereby quickly changing the suspension height of one wheel.