Here’s one short article.
You can connect up to 8 clients to your Genie. It doesn’t matter whether they are wired or wireless, but you can’t connect more than 8. However Only 3 can be active at any one time. If you try to use a fourth one you won’t be able to use live TV or even watch recorded.
This may not be a problem for a large home where people don’t spend time in every room, but if you’re looking for the ability to tune to 8 shows at the same time (for example for a man cave) or if your four kids all like to watch TV in their rooms (I know, what is this, 1976?) then you need to be thinking of other options.
Adding H25 receivers is a good way to give you some backup for live TV watching, but you can still only stream three things from your Genie. Another option is using a tablet or smartphone and DIRECTV on demand to get that same recorded content. That route also gives you over 100 channels of live TV as well.
DIRECTV folks are asked every year if customers can use more than one Genie DVR in the house and so far the answer has been no. There isn’t really a hardware limitation but it’s a matter of re-engineering the software to make it customer-friendly. With two Genies in the home, they compete for the ability to connect to clients and there can be all sorts of chaos. Maybe at some point this will be fixed.