Recording one channel and watching another is supported if both are from same frequency on single tuner box,
Probably on dual tuner you can achieve recording diffrent sat and watch diffrent sat at same time,
May be you have dual output LNB, so two cables.
DiSeqC 4*1 switch you can connect 4 LNB at a time ,
With 8*1 , one can watch 8,
By cascading 4*1 and 8*1 one can even tune 32 diffrent sats,
Based on your budget you can buy, i am not from Europe, so not sure which box people use most.