Once again that depends on what receivers they are. Not all are compatible with SWM. Technically, assuming you have all single tuner (or up to three dual-tuner DVRs) SWM-compatible receivers, you could use a SWM8 at half the price. The only SWM compatible SD receiver IIRC is the D12 (and there are a couple SD DVRs as well - R16, R22, and R23).
The SWM switch (regardless if it is SWM8 or SWM16) requires all four lines from your current dish going in, then you'd run from the SWM switch to an 8 way green label splitter, and each receiver line would go to that splitter. There is also a power injector which can be installed either at the switch location or at a receiver location connected to port #1 on the splitter.
There are two 'Legacy' ports on the SWM8/16 as well, which will allow you to connect up to two non-SWM receivers (or one non-SWM DVR) to the system.
If your receivers are ALL non-SWM, then you're going to need to install a traditional/legacy 4x8 multiswitch. If this is the case and you are out of contract, you should seriously look into retention offers to get upgraded to a newer system with better/HD receivers.
Sent from my Galaxy SII using some Tappity Talkity thing.