as far as i know it records one while watch one my tuners have loop through and can with the loop through cable but this is way above me mate
Any chance of a picture of that tuner mate im curious.
As for how many channels can be recorded at the same time well since a given transponder can carry say 8 maybe more channels on the same TP then it in theory could recored them all if the Hard drive was not a limitation but it is. Ive read upto 16 channel would be the limit of the best hard drives but ive not tested it.