OK. If you cabled up your 501 directly to the 61.5 dish DP single LNB and still got no transponder 10, I'm pretty sure you must have a defective DP single. Note that a 501 can't demodulate 8PSK (what Dish uses for HD), so you will not be able to tune most transponders on 61.5. Let me go check TheList...
Here's the list, according to TheList.

The only transponders left on 61.5 with QPSK modulation are 8, 10, 14, 18, 21, and 29. The rest are either 8PSK or not currently transmitting. Note that a 501 cannot demodulate the 8PSK transponders; it will show zero signal strength even though they're there. Recommend trying transponder 21. If 21 and 29 come in, but the even transponders above do not, then your DP single LNB is not sending it's bandstacked band.