akstockton, if you haven't figured it out yet, and you do in fact have a SuperDish 105 that you want to point at 121, a dish 500 that you want to point at 110 & 119, and a DP34, then you just need a single line off the FSS lnb of the superdish and two lines from the 110/119 feeds from the dish 500.
Generally you want the 119 feed in port 1, 110 in 2, and 121 in 3 of the dp34 but it should work regardless. The switch has no idea that the lines come from different dishs. You don't need a dp21 (sw21 won't work I think anyway?) in the mix unless you're trying to add a 4th bird at 148 or something.
I'm assuming here that you started with a dp500 with a dp21 feeding your receiver, and bought this superdish with a dp34 off ebay, resulting in your current equipment list.
OK, it sounds like he has a 105 SD, and he also has a Dish500 w/ 2 legacy dual LNBs and an SW21. If he uses the SD to get the 121, he will need to take the outrigger DP LNB and put it on the D500. He will also need another DP single LNB or he will need to swap what he has for a DP Twin. Sounds like heis current setup will not work. He will also need a DP+44 switch if he wants to get his locals from the 148, as well as another D300 and DP Single.
Look, If you have your locals. Call E*, tell them you have a SD for the 121, and you need the 148 installed for your locals(if you don't have them, ADD THEM). This will upgrade you to the DP+44 for free, and the installer will probably swap out your 105 head for a 121 OR swap out your legacy duals and SW21 for a DP Twin. May cost you a couple of dollars, but i would say that is your best bet.