I have a similar problem with my Solo2 running VTI 9.0.3 connected to a Harmam/Kardon AVR161S A/V receiver. Every time, I turn off (and then on again) the TV sound disappears and can only be resurrected by powering off/on the box using the switch on the backside (simple reboot is not enough).
I am not clear how this problem started. It worked until yesterday evening and I am not aware of any changes to the box. I certainly have no "unauthorised" plugins running. I originally thought that this might be a problem with the HDMI-CEC link messages. But that does not seem to be the case. I turned HDMI-CEC off on the TV, receiver, and Solo2, but the problem persists. I can also reproduce the same effect by simply pulling out the HDMI cable from the TV and plugging back in. I think that there might be a problem with the enigma2 drivers as this seems to be a problem for VTI and BH.
For the moment, I could work around this by passing the sound through the TosLink (optical) connection rather than the HDMI connection to the AV receiver. But I'd like to reclaim the TosLink port on the receiver for other things. Any help is greatly appreciated.