I can't tell for 6900 Combo, but for 6900 Combo plus you can:
1. watch encoded, record fta at same time (only from same TP, or DVB-S + DVB-T)
2. record fta, watch encoded at same time (only from same TP, or DVB-S + DVB-T)
3. record fta, watch another fta same time (only from same TP, or DVB-S + DVB-T)
new firmware, wich will allow to record 2 channels and watch 3rd one at same time is to come out soon.