I am unable to watch or record from more channels than I think that I should be able to...

I am using a dual DVB-S2 tuner (00-1102709-01) with 2 cables plugged into it. However, when I am recording 1 or 2 encrypted channels from a single transponder frequency, I am able to watch only encrypted channels on the same transponder frequency or a few unencrypted channels on a different transponder frequency.

Shouldn't I be able to watch any other channel while something is being recorded from a certain transponder frequency?

It seems as if only the "Tuner A" is being used. I have tried to swap the cables, still only the "Tuner A" seems to be used all the time, despite any settings to prefer "Tuner B", either for watching, or for recording.

Might "Tuner B" be faulty? The cables seem alright.
I have read somewhere that the the conditional-access module should be able to decrypt as many as 4 encrypted channels, but the statement may have been valid for an older version of the conditional-access module.

Would it help if I added another dual DVB-S2 tuner with another pair of cables?
Or am I hitting some decryption limit?
There has been no message about no free tuners, or anything to that effect. Just black screen and no sound.

I am using OpenViX 5.4.001.