Both you guys can be right. It depends on how the CI is wired. If it is hardwired to tuner 1, we have a problem. This would be a severe design issue though.
It is true however that settop-boxes chose wisely, whether or not they send a TransportStream over the CAM, depending on whether the channel needs descrambling. If channel 1 on tuner 1 does not need descrambling (is FTA), the TS is not routed via the CAM, which can therefore be used for channel 2 on tuner 2.
There are even smarter solutions. Digital Devices can for example remux scrambled channels on multiple tuners into one single TransportStream, which it then sends to the CAM for parallel descrambling. Today's CAMs can descramble up to 32 or even 64 ES PIDs with a bandwidth of up to 100mbps. You can descramble quite some channels in parallel with that. It is even possible to add/remove programs in that mux on-the-fly without introducing glitches.
There is also a CI-PHY from SmarDTV which supports that from 2 tuner inputs. So basically 2 tuners can use one single CAM for descrambling in parallel. I don't even dare asking for something like that. Just for the basics...
Sony's solution in my opinion is no twin-tuner at all. All it can do is watch and record with 2 FTA channels. You can't even record 2 FTA channels, probably because when scheduling the recordings, the TV can't already know whether the events will be scrambled or not.
What I expect from twin-tuner that Sony does not deliver:
- PiP
- parallel recordings
- watch FTA while recording scrambled
