The installation guide that comes with the DPP44 switch does not list any limitations on which satellites can be hooked up. They only recommend that 105/121 be hooked up to the 4th satellite input. The reason they recommend that is that old receivers do not know how to receive 105/121, so they will just see the first 3 satellites.
The 2800, 3900, 4900, 6000 are the only legacy receivers listed as being able to see more than 3 satellites slots. So, when 105/121 is on the forth slot they see it as a SW21/SW64 combo. I can confirm this with my 6000, it sees 119/110/61.5 as a SW64 on side one of a SW21, and it sees 121 on the side 2 of the SW21 (the DPP44 emulates the SW21/SW64 for legacy receivers).
The new receiver that are DishPro compatible have no trouble seeing all 4 satellites and the switch test is just 4 steps as it goes through each of the 4 connections. The DP receivers are all supposed to be able to see 5 satellites if you hook up a DP21 switch in there, but I have not tried this since I only have 4 dishes up at this time.
I have a 821, 6000, and a 301 hooked up with no issues seeing 119/110/61.5/121. My 921 should be here on Friday for me to try out the DPP separator. As far as 61.5/148 at the same time the issue has been duplicate program numbers in the guide, but people report that it has worked in the past, so I would bet it would work with the DPP44. I do not think it is a switch issue, just a confusing guide in the receiver.
I talked to Claude this morning at
http://www.dishstore.net and he still had some DPP44s in stock. He somehow managed to get the entire supply for the area shipped to him