I 100% sure I don't got swm. And wouldn't it need a swm8 switch because each receiver only needs 1 wire to it.
1. You do NOT have an SWM LNB now, but do have an SWM8. If this is the case, there will be four coax from the LNB to the SWM8, and a single coax to your DVR (for 2 tuner operation). There will be a power inserter someplace to power the SWM8. If this is what you have, then the SWM8 will need to be replaced with an SWM16 for your added equipment.
2. You DO have an SWM LNB now, with a single coax coming down from the dish. There is a power inserter someplace as well as a splitter, with one coax going to the DVR and one coax going to the D12. If this is what you have, then the LNB needs to be replaced, and three additional coax need to be brought down from the dish. All four would then go to an SWM16.
3. You do NOT have an SWM LNB, and you do NOT have an SWM8. If this is the case, at least three coax should be coming down from the dish. Two would go to the DVR and one would go to the D12. There would be no power inserter anyplace. If this is what you have, then an SWM16 will need to be installed to support your new configuration.
Edited to add a fourth possibility:
4. You have both a Slimline dish for HD and you have a World direct dish for international programming. In this case you would either have a WB68 multiswitch that both dishes connect to, or an SWM8 that both dishes connect to. In this case, the SWM16 would replace whatever switch is already there.