Sean,
Correct, but since all three tuners are being used you can only flip between ESPN HD, HDNET and ABC-HD or you will have to cancel either a SAT recording (if you're flipping to another SAT channel) or cancel your OTA recording if you wish to flip to say NBC-HD. I am assuming you are in Single User Mode. You can, however, watch a recorded event already on the DVR during this time and not affect the three recordings.
The two SAT tuners in the 942 are fine, but it really needs a 2nd OTA tuner IMO. Hopefully the home server will have 4 Sat and 2 OTA tuners at a minimum.